49.1 Acute Fever, Sepsis Screening & FUO in Primary Care

ABFM Family Medicine Certification Study Guide Exam

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1 Chapter 1: Exam Structure, Blueprint & Clinical Decision-Making

1.1 Exam Blueprint, FMCLA vs. One-Day Exam & Board Scoring 1.2 Clinical Reasoning, Test-Taking Strategy & Ambiguity Management 1.3 Evidence-Based Medicine & Clinical Practice Guidelines in Primary Care

2 Chapter 2: Healthcare Systems, Practice Management & Quality

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3 Chapter 3: Ethics, Law, Biostatistics & Health Equity

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4 Chapter 4: Lifestyle Counseling & Behavior Change

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5 Chapter 5: Nutrition, Physical Activity & Chronic Disease Prevention

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6 Chapter 6: Routine Adult Immunizations

6.1 ACIP Adult Respiratory Vaccines: Influenza, COVID-19, RSV & Pneumococcal 6.2 ACIP Adult Non-Respiratory Vaccines: Tdap, Shingrix, HPV & Hep B 6.3 Immunizations in Special Populations: Pregnancy, Asplenia & Immunocompromise

7 Chapter 7: Pediatric Health Maintenance & Surveillance

7.1 Newborn Examination & Early Postnatal Care 7.2 Well-Child Care, Developmental Surveillance & Milestones 7.3 Pediatric & Adolescent Screening: Vision, Hearing, Anemia & Lead 7.4 Pediatric Oral Health, Dental Screening & Fluoride

8 Chapter 8: Behavioral Health & Safety Screening

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9 Chapter 9: Adult Preventive Screening: Cardiovascular & Metabolic

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10 Chapter 10: Adult Cancer Screening: Breast & Gynecologic

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11 Chapter 11: Adult Cancer Screening: Colorectal, Lung & Prostate

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12 Chapter 12: Sexual Health, Infectious Disease Screening & Contraception

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13 Chapter 13: Reproductive Life Planning, Lactation & Preoperative Care

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14 Chapter 14: Emergent Cardiovascular Conditions

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15 Chapter 15: Cardiac Arrhythmias, Heart Failure & Hypertensive Crises

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16 Chapter 16: Vascular & Thromboembolic Emergencies

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17 Chapter 17: Neurologic Emergencies: Stroke & Altered Consciousness

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18 Chapter 18: Neurologic Trauma & Acute Cranial Emergencies

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19 Chapter 19: Acute Abdominal, Pelvic & Gastrointestinal Emergencies

19.1 Acute Abdominal & Pelvic Pain Triage 19.2 Upper & Lower Gastrointestinal Bleeding 19.3 Acute Hepatic Failure, Cholangitis & Severe Jaundice

20 Chapter 20: Acute Pulmonary & Airway Emergencies

20.1 Acute Hypoxic Respiratory Failure & ARDS 20.2 Severe Community-Acquired Pneumonia & Empyema 20.3 Acute Severe Epistaxis & Airway Obstruction

21 Chapter 21: Acute Traumatic Injuries & Wound Care

21.1 Major Trauma Resuscitation & Initial Assessment 21.2 Burn Assessment, Inhalation Injury & Resuscitation 21.3 Laceration Management, Complex Wounds & Animal Bites

22 Chapter 22: Acute Orthopedic & Musculoskeletal Emergencies

22.1 Acute Ambulatory Fractures & Initial Splinting 22.2 Compartment Syndrome & Major Orthopedic Trauma 22.3 Septic Arthritis & Acute Microcrystalline Crises

23 Chapter 23: Severe Infections, Sepsis & Systemic Emergencies

23.1 Sepsis, Septic Shock & Initial Fluid Resuscitation 23.2 Necrotizing Soft Tissue Infections & Severe CNS Infections 23.3 Anaphylaxis Diagnosis, Epinephrine Dosing & Airway Protection

24 Chapter 24: Metabolic, Endocrine & Electrolyte Emergencies

24.1 Diabetic Ketoacidosis & Hyperosmolar Hyperglycemic State 24.2 Critical Electrolyte Emergencies: Dyskalemias & Dysnatremias 24.3 Severe Calcium Abnormalities & Acute Adrenal Crisis

25 Chapter 25: Hematologic, Urologic & Dental Emergencies

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26 Chapter 26: Psychiatric, Behavioral & Obstetric/Gynecologic Emergencies

26.1 Suicidal Ideation, Acute Agitation & Behavioral Emergencies 26.2 Acute Physical & Sexual Assault Care 26.3 Life-Threatening Vaginal Bleeding & Ectopic Pregnancy 26.4 Environmental Heat Stroke & Severe Hypothermia

27 Chapter 27: Acute Head, Neck & Neurologic Symptoms

27.1 Primary Acute Headaches: Migraine, Tension & Cluster 27.2 Concussion & Minor Closed Head Injury Evaluation 27.3 Transient Ischemic Attack Evaluation & ABCD2 Risk Scoring

28 Chapter 28: Acute Cranial Nerves, Hearing & Sensory Symptoms

28.1 Peripheral Neuropathies: Bell's Palsy, Carpal Tunnel & Radiculopathy 28.2 Acute Tinnitus, Sudden Sensorineural Hearing Loss & Cerumen Impaction 28.3 Acute Dizziness, Benign Paroxysmal Positional Vertigo & Vestibular Neuritis

29 Chapter 29: Acute Upper Respiratory Tract Infections

29.1 Acute Viral Rhinosinusitis vs. Bacterial Rhinosinusitis 29.2 Acute Pharyngitis: Group A Streptococcus & Centor Criteria 29.3 Acute Otitis Media, Otitis Externa & Serous Effusion

30 Chapter 30: Acute Lower Respiratory Infections & Cough

30.1 Influenza, COVID-19 & Viral Respiratory Syndromes 30.2 Acute Bronchitis & Lower Respiratory Tract Infections 30.3 Ambulatory Community-Acquired Pneumonia

31 Chapter 31: Allergic, Nasal & Non-Infectious Pulmonary Conditions

31.1 Allergic Rhinitis & Acute Non-Anaphylactic Allergic Reactions 31.2 Acute Dyspnea in Ambulatory Care 31.3 Interstitial Lung Diseases & Sarcoidosis Presentation

32 Chapter 32: Acute Chest, Cardiac & Vascular Symptoms

32.1 Palpitations Evaluation & Arrhythmia Triage in Primary Care 32.2 Deep Vein Thrombosis & Superficial Thrombophlebitis 32.3 Ambulatory Hypotension & Orthostasis Evaluation

33 Chapter 33: Acute Upper Gastrointestinal Conditions

33.1 Peptic Ulcer Disease & Gastritis 33.2 Dysphagia, Esophagitis & Acute Esophageal Disorders 33.3 Acute Nausea, Vomiting & Foodborne Illness

34 Chapter 34: Acute Lower Gastrointestinal Conditions

34.1 Acute Infectious Diarrhea & Gastroenteritis 34.2 Acute Constipation & Functional Bowel Changes 34.3 Ano-Rectal Disorders: Hemorrhoids, Fissures, Abscesses & Pruritus Ani

35 Chapter 35: Inflammatory, Functional & Malabsorptive GI Disorders

35.1 Acute Flares of Inflammatory Bowel Disease 35.2 Irritable Bowel Syndrome: Diagnosis, Subtyping & Management 35.3 Celiac Disease & Malabsorption Syndromes

36 Chapter 36: Acute Abdominal, Hepatic & Biliary Disorders

36.1 Ambulatory Abdominal & Pelvic Pain Triage 36.2 Acute Cholecystitis, Biliary Colic & Pancreatitis 36.3 Acute Liver Injury & Viral Hepatitis

37 Chapter 37: Acute Abdominal Wall, Hernias & Dental Conditions

37.1 Abdominal Wall, Inguinal & Ventral Hernias 37.2 Acute Dental Pain, Odontogenic Abscess & Aphthous Ulcers 37.3 Acute Edema: Unilateral vs. Bilateral Diagnostic Evaluation

38 Chapter 38: Acute Infectious Dermatoses

38.1 Bacterial Skin Infections: Impetigo, Cellulitis & Cutaneous Abscesses 38.2 Fungal Skin Infections: Tinea Corporis, Cruris, Pedis & Onychomycosis 38.3 Viral Cutaneous Infections: Herpes Simplex, Zoster & Molluscum Contagiosum

39 Chapter 39: Inflammatory, Allergic & Autoimmune Dermatoses

39.1 Atopic Dermatitis, Contact Dermatitis & Eczematous Flares 39.2 Non-Infectious Rashes: Urticaria, Drug Eruptions & Erythema Multiforme 39.3 Cutaneous Malignancies & Premalignant Lesions: AK, BCC, SCC & Melanoma

40 Chapter 40: Acute Shoulder, Elbow & Upper Extremity Injuries

40.1 Rotator Cuff Pathology, Tendinopathy & Shoulder Impingement 40.2 Lateral & Medial Epicondylitis, Olecranon Bursitis & Elbow Sprains 40.3 Wrist & Hand Soft-Tissue Injuries: De Quervain, TFCC & Finger Sprains

41 Chapter 41: Acute Knee, Ankle & Lower Extremity Injuries

41.1 Meniscal Tears, Ligamentous Knee Injuries & Patellofemoral Pain 41.2 Ankle Sprains, Ottawa Ankle Rules & Achilles Tendinopathy 41.3 Plantar Fasciitis, Shin Splints & Overuse Syndromes

42 Chapter 42: Acute Ambulatory Fractures & Dislocations

42.1 Distal Radius, Scaphoid & Common Upper Extremity Fractures 42.2 Metatarsal, Clavicle & Common Lower Extremity Fractures 42.3 Joint Dislocation Management: Nursemaid's Elbow & Shoulder Subluxation

43 Chapter 43: Acute Axial Musculoskeletal Pain & Falls

43.1 Acute Low Back Pain: Red Flags, Strain & Disc Herniation 43.2 Acute Cervical Strain, Whiplash & Axial Neck Pain 43.3 Evaluation of Falls in Ambulatory & Older Patients

44 Chapter 44: Acute Inflammatory Arthropathies & Generalized Pain

44.1 Acute Inflammatory Arthritis & Spondyloarthropathies 44.2 Myalgias, Rhabdomyolysis & Post-Viral Pain Syndromes 44.3 Acute Non-Headache Pain Management Strategies

45 Chapter 45: Acute Renal, Urinary & Genitourinary Conditions

45.1 Uncomplicated UTI, Pyelonephritis & Acute Urethritis 45.2 Hematuria Workup & Glomerulonephritis 45.3 Nephrolithiasis & Acute Urinary Tract Obstruction

46 Chapter 46: Acute Male Genitourinary & Prostatic Conditions

46.1 Acute Prostatitis, Epididymitis & Orchitis 46.2 Acute Scrotal Pain: Torsion vs Appendage, BPH & Male Genital Emergencies 46.3 Acute Urinary Retention & Incontinence Evaluation

47 Chapter 47: Acute Women's Health & Early Pregnancy Care

47.1 Early Pregnancy Diagnosis, Dating & Initial Complications 47.2 Abnormal Uterine Bleeding & Acute Menstrual Disorders 47.3 Premenstrual Syndrome & Premenstrual Dysphoric Disorder

48 Chapter 48: Breast Disorders, STIs & Pediatric Elimination

48.1 Palpable Breast Mass, Mastitis & Nipple Discharge 48.2 Sexually Transmitted Infections: Diagnosis, Staging & CDC Guidelines 48.3 Pediatric Enuresis & Encopresis

49 Chapter 49: Systemic Signs, Metabolic Dysregulation & Miscellaneous Infections

49.1 Acute Fever, Sepsis Screening & FUO in Primary Care 49.2 Acute Hyperglycemia & Symptomatic Hypoglycemia 49.3 Electrolyte Abnormalities: Mild-to-Moderate Disturbances 49.4 Vector-Borne, Tick-Borne & Rickettsial Illnesses

50 Chapter 50: Chronic Cardiovascular Diseases: Hypertension & Ischemia

50.1 Essential Hypertension Management: 2025 AHA/ACC Guideline & JNC Strategies 50.2 Chronic Coronary Artery Disease & Post-MI Secondary Prevention 50.3 Chronic Heart Failure: HFrEF, HFpEF & Quadruple GDMT

51 Chapter 51: Chronic Vascular, Valvular & Dyslipidemic Diseases

51.1 Peripheral Arterial Disease & Claudication 51.2 Chronic Valvular Heart Disease & Murmur Evaluation 51.3 Lipid Disorders & ASCVD Risk-Based Statin Therapy

52 Chapter 52: Chronic Respiratory Diseases: Asthma & COPD

52.1 Chronic Asthma Management: GINA Stepwise SMART Therapy 52.2 Chronic Obstructive Pulmonary Disease: GOLD Recommendations 52.3 Solitary Pulmonary Nodule Evaluation & Fleischner Society Criteria

53 Chapter 53: Chronic Metabolic Diseases: Diabetes Mellitus

53.1 Type 2 Diabetes Management: ADA Pharmacotherapy Algorithms 53.2 Type 1 Diabetes: Basal-Bolus Insulin, CGMs & Diabetic Complications 53.3 Diabetic Microvascular & Macrovascular Disease Surveillance

54 Chapter 54: Obesity, Nutrition & Metabolic Bone Diseases

54.1 Medical & Behavioral Management of Obesity & Incretin Mimetics 54.2 Osteoporosis & Metabolic Bone Disease: DEXA, FRAX & Antiresorptives 54.3 Nutritional Deficiencies: Vitamin D, B12, Iron & Malnutrition

55 Chapter 55: Chronic Endocrine Disorders

55.1 Primary & Subclinical Hypothyroidism, Hyperthyroidism & Nodules 55.2 Adrenal Disorders: Addison's Disease & Cushing's Syndrome 55.3 Hypercalcemia, Hyperparathyroidism & Pituitary Disorders

56 Chapter 56: Chronic Kidney Disease & Venous Disorders

56.1 Chronic Kidney Disease: KDIGO Staging & Renoprotective Therapy 56.2 Chronic Venous Insufficiency, Stasis Dermatitis & Lymphedema 56.3 Chronic Electrolyte & Acid-Base Management in CKD

57 Chapter 57: Chronic Gastrointestinal & Hepatic Diseases

57.1 Gastroesophageal Reflux Disease, Barrett's Esophagus & Dyspepsia 57.2 Chronic Liver Disease: MASLD/NAFLD, Cirrhosis & Portal Hypertension 57.3 Viral Hepatitis B & C: Long-Term Monitoring & DAA Therapy

58 Chapter 58: Colorectal Surveillance & Chronic Pancreaticobiliary Care

58.1 Post-Polypectomy Colorectal Polyp Surveillance Guidelines 58.2 Chronic Pancreatitis & Exocrine Pancreatic Insufficiency 58.3 Chronic Nausea, Gastroparesis & Functional GI Disorders

59 Chapter 59: Chronic Musculoskeletal & Rheumatologic Disorders

59.1 Osteoarthritis: Hip, Knee & Hand Management 59.2 Spinal Conditions: Spinal Stenosis, Spondylolisthesis & Compression Fractures 59.3 Chronic Myopathies & Fibromyalgia Syndrome

60 Chapter 60: Chronic Neurologic & Neurodegenerative Disorders

60.1 Dementia: Alzheimer's, Vascular & Lewy Body Disease 60.2 Parkinson's Disease & Essential Tremor 60.3 Epilepsy: Chronic Antiseizure Medications & Post-Stroke Care

61 Chapter 61: Chronic Peripheral Nerves, Pain & Sensory Disorders

61.1 Diabetic & Chronic Peripheral Neuropathies 61.2 Chronic Pain Syndromes & Chronic Daily Headaches 61.3 Chronic Tinnitus, Presbycusis & Persistent Dizziness

62 Chapter 62: Chronic Psychiatric Disorders

62.1 Major Depressive Disorder & Generalized Anxiety Disorder 62.2 Bipolar Disorder: Maintenance Pharmacotherapy & Lithium Monitoring 62.3 Adult & Pediatric Attention-Deficit/Hyperactivity Disorder

63 Chapter 63: Chronic Behavioral Health & Neurodevelopmental Conditions

63.1 Chronic Behavioral Conditions: PTSD, OCD & Somatization 63.2 Autism Spectrum Disorder & Intellectual Disabilities 63.3 Eating Disorders: Anorexia Nervosa, Bulimia & Binge Eating

64 Chapter 64: Chronic Substance Use Disorders & Tobacco Cessation

64.1 Alcohol Use Disorder: Pharmacotherapy & Relapse Prevention 64.2 Opioid & Stimulant Use Disorders: MOUD & Harm Reduction 64.3 Longitudinal Tobacco Cessation Pharmacotherapy

65 Chapter 65: Chronic Dermatologic Conditions

65.1 Acne Vulgaris, Rosacea & Seborrheic Dermatitis 65.2 Chronic Plaque Psoriasis & Biologic Therapies 65.3 Chronic Eczema, Hidradenitis Suppurativa & Cutaneous Lupus

66 Chapter 66: Chronic Reproductive, Infectious & Geriatric Special Care

66.1 Chronic Menstrual Disorders, Infertility & Sexual Dysfunction 66.2 Menopause Management & Hormone Replacement Therapy 66.3 Chronic HIV Infection Management & Primary Care Integration 66.4 Gender-Affirming Primary Care & Hormone Therapy 66.5 Advance Care Planning, Palliative Care & End-of-Life Symptom Control

67 Chapter 67: Continuity Care: Sleep, Fatigue, Cancer, Pregnancy & the Adult Preventive Visit

67.1 Chronic Insomnia & Obstructive Sleep Apnea 67.2 Chronic Malaise, Fatigue & ME/CFS 67.3 Primary Care During Cancer Treatment & Survivorship 67.4 Routine Prenatal Care & Longitudinal Pregnancy Management 67.5 The Periodic Adult Health Examination & Medicare Annual Wellness Visit

49.1 Acute Fever, Sepsis Screening & FUO in Primary Care

Key Takeaways Explain This Topic AI

Fever is a regulated physiological elevation of the hypothalamic thermoregulatory set-point mediated by pyrogenic cytokines (IL-1, IL-6, TNF-alpha) stimulating endothelial prostaglandin E2 (PGE2) synthesis via cyclooxygenase-2 (COX-2); in contrast, hyperthermia represents an uncontrolled failure of peripheral heat dissipation with an unchanged hypothalamic set-point, rendering antipyretics ineffective and necessitating active external cooling.

Under the Sepsis-3 consensus, sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection; the quick Sequential Organ Failure Assessment (qSOFA) serves as an ambulatory screening tool where a score >=2 (respiratory rate >=22 breaths/min, altered mental status [GCS <15], systolic BP <=100 mmHg) identifies patients at high risk of in-hospital mortality requiring emergent transfer and ICU evaluation.

The Surviving Sepsis Campaign 'Hour-1 Bundle' mandates five immediate interventions: measure blood lactate (remeasure in 2-4 hours if >2 mmol/L), obtain blood cultures prior to antibiotic administration, administer broad-spectrum IV antimicrobials within 60 minutes, infuse a rapid crystalloid bolus of 30 mL/kg for hypotension or lactate >=4 mmol/L, and initiate vasopressors (norepinephrine first-line) to maintain a mean arterial pressure (MAP) >=65 mmHg.

Classic Fever of Unknown Origin (FUO), defined by Durack and Street, requires documented temperatures >38.3°C (>101°F) on multiple occasions over >3 weeks without diagnosis after 1 week of inpatient evaluation or 3 outpatient visits; etiologies comprise infections (30-40%: occult abscesses, endocarditis, osteomyelitis, tuberculosis), neoplasms (20-30%: lymphoma, renal cell carcinoma), non-infectious inflammatory disorders (15-20%: Giant Cell Arteritis/PMR in elderly, Adult-onset Still disease with ferritin >3000-10000 ng/mL), and miscellaneous causes (10-15%: drug fever, subacute thyroiditis, factitious fever).

Adult-Onset Still Disease (AOSD) is characterized by the classic triad of daily quotidian spiking fevers, an evanescent salmon-pink maculopapular rash coinciding with fever spikes, and polyarthritis, supported by dramatic hyperferritinemia (>3000 to >10,000 ng/mL) with negative ANA and RF.

Last updated: September 2026

Thermoregulation: Fever vs. Hyperthermia

Body temperature in humans is precisely regulated by the preoptic area of the anterior hypothalamus, which maintains a thermal equilibrium or "set-point" between 36.5°C and 37.5°C (97.7°F to 99.5°F). Pathologic elevations in body core temperature fall into two distinct pathophysiologic entities: pyrogenic fever and hyperthermia .

Molecular Pathophysiology of Fever

Fever represents a regulated elevation of the hypothalamic thermostatic set-point initiated by pyrogenic stimuli:

Exogenous Pyrogens : Microbial products, notably bacterial lipopolysaccharide (LPS/endotoxin from Gram-negative bacteria) or lipoteichoic acid and peptidoglycans from Gram-positive organisms, stimulate host immune cells via Toll-like receptors (TLRs).

Endogenous Pyrogenic Cytokines : Activated monocytes, tissue macrophages, and endothelial cells synthesize and release endogenous pyrogens, primarily interleukin-1 (IL-1beta) , tumor necrosis factor-alpha (TNF-alpha) , and interleukin-6 (IL-6) .

Hypothalamic Transduction : These circulating cytokines travel to the fenestrated capillary network of the organum vasculosum of the lamina terminalis (OVLT) , a circumventricular organ bordering the anterior hypothalamus that lacks a tight blood-brain barrier. Cytokines bind to endothelial receptors, inducing the expression of cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1.

Prostaglandin E2 (PGE2) Synthesis & Set-Point Shift : Endothelial cells release PGE2, which diffuses across into adjacent hypothalamic glial and neural tissue, binding to EP3 prostanoid receptors on thermoregulatory neurons in the preoptic area. This receptor activation suppresses warm-sensitive neurons and stimulates cold-sensitive neurons, effectively elevating the hypothalamic thermostatic set-point to a higher level (e.g., 38.5°C to 40.0°C).

Thermoregulatory Efferent Responses : Perceiving the current body temperature as abnormally cold relative to the new elevated set-point, the hypothalamus coordinates autonomic and behavioral heat conservation mechanisms: peripheral vasoconstriction (pale, cool extremities), involuntary rhythmic muscular contractions ( shivering / rigors ), and behavioral seeking of warmth (curling up, bundling in blankets). Once the elevated set-point is reached, shivering ceases, and core temperature remains stabilized at the higher level.

Defervescence : When pyrogenic cytokines subside or antipyretics are administered, the set-point resets downward to normal (37.0°C). The hypothalamus initiates active heat dissipation mechanisms: cutaneous vasodilation (flushing) and profuse diaphoresis ("the fever breaks"). MOLECULAR CASCADE OF PYROGENIC FEVER

• Exogenous Pyrogens (Bacterial LPS, Viral Antigens, Peptidoglycan)
• │
• ▼
• Monocytes / Macrophages Activation ──► IL-1β, TNF-α, IL-6 Release
• │
• ▼
• Circulation to Organum Vasculosum Laminae Terminalis (OVLT)
• │
• ▼
• Endothelial COX-2 Induction ──► Prostaglandin E2 (PGE2) Synthesis
• │
• ▼
• EP3 Receptor Activation in Preoptic Anterior Hypothalamus
• │
• ▼
• UPWARD RESETTING OF THERMOSTATIC SET-POINT (e.g., 37°C ──► 39°C)
• ├── Heat Conservation: Peripheral Vasoconstriction (chills)
• └── Heat Production: Involuntary Shivering / Rigors
• Hyperthermia: Failure of Thermoregulation

In contrast to fever, hyperthermia is characterized by an unchanged, normal hypothalamic set-point accompanied by an uncontrolled, life-threatening rise in core body temperature due to either excessive endogenous heat production , overwhelming environmental heat absorption , or impaired peripheral heat dissipation .

Because the hypothalamic set-point is normal, hypothalamic efferent mechanisms are actively striving to cool the body (maximal cutaneous vasodilation, intense sweating), but physiological mechanisms are overwhelmed or exhausted.

Caution

CRITICAL PHARMACOLOGIC PEARL: ANTIPYRETICS IN HYPERTHERMIA Antipyretic agents (acetaminophen, ibuprofen, aspirin) act exclusively by inhibiting hypothalamic COX-2 and blocking PGE2 synthesis to lower an elevated thermostatic set-point.

In hyperthermia, because the hypothalamic set-point is already normal, antipyretics are completely ineffective and potentially harmful (increasing risks of acetaminophen hepatotoxicity or NSAID-induced acute tubular necrosis in dehydrated, rhabdomyolysis-prone patients). Management requires immediate, active physical cooling (conductive and evaporative cooling) and etiology-specific pharmacotherapy.

Major Clinical Hyperthermia Syndromes

Heat Stroke : Core temperature >40.0°C (>104.0°F) associated with profound central nervous system dysfunction (delirium, ataxia, seizures, coma) and multiorgan failure. Classified as classic (non-exertional) heat stroke (elderly, frail patients with impaired mobility in heatwaves; anhidrosis often present) or exertional heat stroke (young athletes, military recruits, outdoor laborers performing vigorous exercise in warm/humid environments; profuse sweating frequently persists). First-line treatment is immediate ice-water immersion cooling (reducing temperature to <39°C within 30 minutes).

Neuroleptic Malignant Syndrome (NMS) : Idiosyncratic life-threatening reaction to dopamine D2 receptor antagonists (high-potency typical antipsychotics like haloperidol, fluphenazine; atypical antipsychotics; antiemetics like metoclopramide) or abrupt cessation of dopaminergic agonists (in Parkinson disease). Characterized by the tetrad of severe hyperthermia , generalized "lead-pipe" muscle rigidity , autonomic instability (labile hypertension, tachycardia, tachypnea, diaphoresis), and altered mental status . Laboratory hallmark: marked elevation in serum creatine kinase (CK often >1,000 to >50,000 U/L) and leukocytosis. Treatment: immediately discontinue offending neuroleptic, aggressive ICU supportive care, IV fluids, and pharmacotherapy with dantrolene (ryanodine channel blocker) or bromocriptine (dopamine agonist).

Serotonin Syndrome (Toxicity) : Acute hyper-serotonergic toxidrome caused by excess serotonergic agonism, classically resulting from drug interactions (e.g., SSRIs/SNRIs combined with MAOIs, tramadol, linezolid, dextromethorphan, triptans, or St. John's wort). Diagnosed via the validated Hunter Serotonin Toxicity Criteria : in the presence of a serotonergic agent, spontaneous clonus; OR inducible clonus with agitation or diaphoresis; OR ocular clonus with agitation or diaphoresis; OR tremor with hyperreflexia; OR hypertonia with temperature >38°C plus ocular or inducible clonus. Key diagnostic differentiators from NMS: hyperreflexia and neuromuscular clonus (predominantly in lower extremities) rather than "lead-pipe" rigidity, rapid onset within hours (vs. days-to-weeks in NMS), and gastrointestinal hypermotility (cramping, hyperactive bowel sounds, diarrhea).

Malignant Hyperthermia (MH) : Autosomal dominant pharmacogenetic disorder of skeletal muscle excitation-contraction coupling, most commonly involving mutations in the ryanodine receptor 1 (RYR1) gene. Triggered by exposure to potent volatile inhalational anesthetics (halothane, isoflurane, sevoflurane, desflurane) or the depolarizing neuromuscular blocker succinylcholine . Uncontrolled calcium release from the sarcoplasmic reticulum triggers sustained muscle contraction, explosive hypermetabolism, hypercapnia (rising end-tidal CO2 despite hyperventilation is the earliest sign), masseter muscle spasm, rapid hyperthermia (rising 1°C every 5 minutes), rhabdomyolysis, severe metabolic acidosis, and hyperkalemic cardiac arrest. Definitive treatment: immediate cessation of triggering agents, hyperventilation with 100% O2, and rapid IV administration of Dantrolene sodium (2.5 mg/kg IV initial bolus, repeated until hypermetabolism ceases). COMPARISON OF HYPERTHERMIA SYNDROMES

• Syndrome Etiology / Triggers Key Neuromuscular Signs Specific Treatment
• ═════════════════════════════════════════════════════════════════════════════════════════════
• Heat Stroke Environmental exposure Ataxia, flaccidity, coma, Ice water immersion;
• or intense exertion seizures; NO rigidity evaporative cooling

• NMS Dopamine D2 antagonists "Lead-pipe" severe rigidity, Dantrolene or
• (antipsychotics) bradykinesia, hyporeflexia Bromocriptine

• Serotonin Serotonergic drug excess Hyperreflexia, clonus, Cyproheptadine,
• Syndrome (SSRIs, MAOIs, linezolid) ocular clonus, tremor Benzodiazepines

• Malignant Volatile anesthetics Masseter jaw spasm, Dantrolene sodium
• Hyperthermia or Succinylcholine generalized muscle rigidity IV (2.5 mg/kg)
• ═════════════════════════════════════════════════════════════════════════════════════════════
• Sepsis Screening & Early Resuscitation in Primary Care

Sepsis represents one of the leading causes of acute mortality worldwide. In ambulatory, urgent care, and primary care clinic settings, recognizing the early signs of sepsis is critical, as every hour of delayed antimicrobial therapy significantly increases mortality.

Sepsis-3 Consensus Definitions

The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) redefined the condition:

Sepsis : Defined as life-threatening organ dysfunction caused by a dysregulated host response to infection . In hospital and ICU settings, organ dysfunction is formally quantified by an acute change in total Sequential Organ Failure Assessment (SOFA) score of >=2 points attributable to the infection, which reflects an in-hospital mortality risk exceeding 10%.

Septic Shock : A subset of sepsis in which underlying circulatory and cellular/metabolic abnormalities are profound enough to substantially increase mortality. Clinically defined by persistent hypotension requiring vasopressors to maintain a mean arterial pressure (MAP) >=65 mmHg AND a serum lactate level >2.0 mmol/L (18 mg/dL) despite adequate fluid resuscitation (mortality >40%).

Ambulatory Risk Stratification: qSOFA vs. SIRS Criteria

Because calculating a full SOFA score requires laboratory values (PaO2, platelets, bilirubin, creatinine) unavailable during initial outpatient triage, the Sepsis-3 task force introduced the quick SOFA (qSOFA) as an actionable bedside risk-stratification tool. THE qSOFA SCREENING CRITERIA

• Clinical Parameter Threshold Value Points Assigned
• ─────────────────────────────────────────────────────────────────────────────
• Respiratory Rate (RR) >= 22 breaths per minute 1 point
• Altered Mental Status Glasgow Coma Scale < 15 1 point
• Systolic Blood Pressure (SBP) <= 100 mmHg 1 point
• ─────────────────────────────────────────────────────────────────────────────
• A qSOFA score >= 2 identifies infected patients at high risk of in-hospital

mortality and ICU admission, warranting immediate transfer to an Emergency Dept.

Systemic Inflammatory Response Syndrome (SIRS) :

Historically, sepsis was defined as SIRS plus suspected infection. SIRS requires >=2 of the following 4 criteria :

• Core temperature >38.0°C (100.4°F) or <36.0°C (96.8°F);
• Heart rate >90 beats/min;
• Respiratory rate >20 breaths/min OR PaCO2 <32 mmHg;

White blood cell count >12,000/mcL, <4,000/mcL, OR >10% immature band forms.

Clinical Utility & Nuance :

SIRS is highly sensitive but non-specific ; many ambulatory patients with uncomplicated viral infections or non-infectious inflammatory triggers (pancreatitis, trauma, exercise) meet SIRS criteria.

qSOFA is less sensitive but highly specific for adverse outcomes and organ dysfunction. An ambulatory patient with suspected infection and a qSOFA score >=2 must NEVER be treated as an outpatient; they require immediate 911 activation and emergency department transfer.

The Surviving Sepsis Campaign "Hour-1 Bundle"

Once sepsis is recognized, the international Surviving Sepsis Campaign guidelines mandate initiation of resuscitation bundle elements within 1 hour of triage:

Measure Blood Lactate Level : Elevated lactate (>2.0 mmol/L) reflects anaerobic metabolism and tissue hypoperfusion. A lactate >=4.0 mmol/L indicates severe metabolic stress and tissue dysoxia. Remeasure lactate within 2 to 4 hours to guide resuscitation (targeting lactate clearance).

Obtain Blood Cultures Prior to Antibiotics : Draw at least two sets of peripheral blood cultures (aerobic and anaerobic) from distinct venipuncture sites. Do not delay antimicrobial initiation by >45 minutes if blood cultures cannot be rapidly obtained.

Administer Broad-Spectrum Intravenous Antimicrobials : Initiate broad-spectrum empiric IV antimicrobials covering Gram-positive and Gram-negative pathogens within 1 hour of recognition.

Rapid Intravenous Crystalloid Resuscitation : Administer a minimum of 30 mL/kg of balanced intravenous crystalloids (e.g., Lactated Ringer's or Plasmalyte) within the first 3 hours for patients with hypotension (mean arterial pressure <65 mmHg) OR initial serum lactate >=4.0 mmol/L .

Vasopressor Therapy : If the patient remains hypotensive during or immediately following the 30 mL/kg fluid bolus, initiate vasopressors to maintain MAP >=65 mmHg . Norepinephrine is the first-line vasopressor of choice (titrated to MAP >=65 mmHg); vasopressin (0.03 units/min) can be added as a second-line agent.

Fever of Unknown Origin (FUO): Diagnostic Strategy

Fever of unknown origin presents one of the most intellectually rigorous diagnostic dilemmas in primary care and internal medicine.

The Classic Definition of FUO

Originally formulated by Petersdorf and Beeson in 1961 and refined by Durack and Street in 1991, classic FUO requires meeting all three of the following criteria:

• Documented body temperature >38.3°C (>101.0°F) on multiple separate occasions;
• Fever duration exceeding 3 weeks ;

Failure to reach a definitive diagnosis despite 1 week of intensive inpatient investigation OR after 3 outpatient clinical visits (or 3 days of focused outpatient testing).

(Note: Durack and Street also classified three additional distinct FUO subtypes: Nosocomial FUO, Neutropenic FUO [ANC <500/mcL], and HIV-associated FUO, each possessing different etiologic spectra and requiring tailored workups). THE FOUR MAJOR ETIOLOGIC CATEGORIES OF FUO

• Etiologic Category Approximate Frequency Prototypic Diagnoses
• ═════════════════════════════════════════════════════════════════════════════════════════
• Infections 30% to 40% Occult intra-abdominal/pelvic abscess,
• infective endocarditis, osteomyelitis,
• extrapulmonary/miliary TB, EBV/CMV

• Neoplasms 20% to 30% Non-Hodgkin lymphoma, Hodgkin lymphoma,
• leukemia, Renal Cell Carcinoma (RCC),
• atrial myxoma, hepatocellular carcinoma

• Non-Infectious 15% to 20% Giant Cell Arteritis (GCA) / PMR,
• Inflammatory Disorders Adult-Onset Still Disease (AOSD),
• (Connective Tissue/Auto) SLE, Polyarteritis nodosa, RA

• Miscellaneous / Other 10% to 15% Drug fever, subacute thyroiditis (de
• Quervain), DVT/PE, factitious fever
• ═════════════════════════════════════════════════════════════════════════════════════════
• Note: In up to 10% to 20% of modern FUO evaluations, no definitive etiology is found
• despite exhaustive workup; the majority of these undiagnosed patients experience benign

spontaneous resolution over time.

Infectious Etiologies (30-40%)

Occult Pyogenic Abscesses : Intra-abdominal (subphrenic, diverticular, appendiceal, hepatic pyogenic abscesses), pelvic (tubo-ovarian), or retroperitoneal/perinephric abscesses. Often insidious in diabetics or elderly patients without localized peritoneal signs.

Infective Endocarditis (IE) : Subacute bacterial endocarditis caused by Streptococcus viridans , Enterococcus faecalis , or indolent HACEK organisms ( Haemophilus , Aggregatibacter , Cardiobacterium , Eikenella , Kingella ). May present with culture-negative endocarditis ( Bartonella , Coxiella burnetii [Q fever], Chlamydia ).

Mycobacterial Infection : Miliary or extrapulmonary tuberculosis (skeletal Pott disease, renal TB, tuberculous peritonitis). Tuberculin skin tests and interferon-gamma release assays (IGRAs) can be falsely negative in disseminated or anergic disease.

Osteomyelitis : Particularly vertebral osteomyelitis or infected spinal hardware, presenting with low back pain and elevated inflammatory markers.

Systemic Viral Infections : Cytomegalovirus (CMV), Epstein-Barr virus (EBV), and acute human immunodeficiency virus (HIV) seroconversion syndrome.

Neoplastic Etiologies (20-30%)

Lymphomas : Both Hodgkin lymphoma (classically displaying Pel-Ebstein fevers —cyclical high fevers for 1-2 weeks alternating with afebrile periods) and Non-Hodgkin lymphoma. Characterized by "B symptoms" (fevers, drenching night sweats, involuntary weight loss >10% over 6 months).

Renal Cell Carcinoma (RCC) : Paraneoplastic fever is observed in up to 20% of RCC cases, mediated by tumor production of IL-6. The classic triad (hematuria, flank pain, palpable mass) is present in <10%; paraneoplastic signs include erythrocytosis, hypercalcemia, and hepatic dysfunction without metastases (Stauffer syndrome).

Leukemias & Myelodysplastic Syndromes : Acute and chronic leukemias.

Atrial Myxoma : Benign cardiac neoplasm producing IL-6, causing fevers, weight loss, elevated ESR, embolic phenomena, and an auscultatory "tumor plop" mimicking mitral stenosis.

Non-Infectious Inflammatory Disorders (15-20%)

Giant Cell Arteritis (GCA) / Polymyalgia Rheumatica (PMR) :

The most frequent rheumatologic cause of FUO in adults aged >=50 years .

Clinical features: Unilateral throbbing temporal headache, scalp tenderness (pain when combing hair), jaw claudication (ischemic fatigue of masseter muscles while chewing, highly specific), polymyalgia symptoms (bilateral morning shoulder and hip girdle aching), and amaurosis fugax or sudden visual loss.

Laboratory findings: ESR markedly elevated (almost universally >50 mm/h, frequently >100 mm/h) and elevated CRP.

Immediate mandate: If GCA is suspected, initiate high-dose systemic corticosteroid therapy immediately (prednisone 40-60 mg daily) to prevent irreversible ischemic optic neuropathy and bilateral permanent blindness. Do NOT wait for a temporal artery biopsy.

Adult-Onset Still Disease (AOSD) :

Severe systemic inflammatory disorder characterized by the Yamaguchi criteria:

Quotidian Spiking Fevers : Daily high spiking fevers (typically peaking in late afternoon or evening >39°C [102.2°F]) that return to baseline between spikes.

Evanescent Rash : An evanescent, non-pruritic, salmon-pink maculopapular rash that characteristically erupts on the trunk and proximal extremities during the fever spike and rapidly fades when temperature normalizes.

Arthralgias / Arthritis : Transient or persistent inflammatory polyarthritis.

Leukocytosis : Marked neutrophilic leukocytosis (WBC >=10,000/mcL with >=80% neutrophils).

Extreme Hyperferritinemia : Serum ferritin concentrations are dramatically elevated, frequently exceeding 3,000 to >10,000 ng/mL (normal <300 ng/mL), with a glycosylated ferritin fraction <20%.

Seronegativity : Antinuclear antibodies (ANA) and Rheumatoid Factor (RF) are characteristically negative.

Miscellaneous Etiologies (10-15%)

Drug Fever :

An underdiagnosed hypersensitivity reaction occurring days to months after drug initiation. Offending agents commonly include beta-lactam antibiotics , sulfonamides , anticonvulsants (phenytoin, carbamazepine), antiarrhythmics (procainamide, quinidine), heparin , and allopurinol .

Clinical clues: Patient often appears paradoxically comfortable despite high fevers; relative bradycardia (Faget sign) may be present; mild peripheral eosinophilia occurs in only 20-30%.

Definitive diagnosis & cure: Rapid defervescence occurs within 48 to 72 hours of discontinuing the offending drug .

Subacute Granulomatous Thyroiditis (de Quervain) : Post-viral inflammatory thyroiditis presenting with anterior neck pain, exquisitely tender goiter, elevated ESR, and suppressed TSH with low radioactive iodine uptake.

Venous Thromboembolism : Occult deep vein thrombosis (DVT) or recurrent micro-pulmonary emboli (PE) inducing low-grade fevers.

Factitious Fever : Feigned or self-induced fevers (pathomimicry). Red flags: Absence of normal diurnal body temperature variation; lack of shivering or diaphoresis during abrupt temperature changes; discrepancy between oral temperature and freshly voided urine temperature (urine temperature normally matches or slightly exceeds core oral temperature); normal resting heart rate despite recorded oral temperature >39.5°C; multiple hospital presentations across different health systems.

Loading diagram... Systematic Diagnostic Algorithm for Fever of Unknown Origin (FUO)