Study guide
10.6 Motor Neuron Disease & Acute Peripheral Neuropathy
ABIM Internal Medicine Exam
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1 Chapter 0: The ABIM Exam, Blueprint & Study Strategy
0.1 Exam Format, Question Types & the 2026 Blueprint 0.2 Eligibility, Registration, Fees & Exam-Day Logistics 0.3 Scoring, the Passing Standard & Score Reports 0.4 Building a Blueprint-Weighted Study Plan
2 Chapter 1: Cardiovascular Disease (14% of Exam)
1.1 Ischemic Heart Disease & Acute Coronary Syndromes 1.2 Antithrombotic Therapy, Secondary Prevention & Mechanical Complications of MI 1.3 Atrial Fibrillation, Atrial Flutter & Stroke Prevention 1.4 Supraventricular Tachycardias, Ventricular Arrhythmias & Bradycardias 1.5 Heart Failure: Classification, Staging & Guideline-Directed Medical Therapy 1.6 Device Therapy, HFpEF & the Cardiomyopathies 1.7 Valvular Heart Disease & Endocarditis Prophylaxis 1.8 Pericardial Disease & Acute Aortic Syndromes 1.9 Hypertension: Classification, Diagnosis & Secondary Causes 1.10 Hypertensive Crises & Dyslipidemia 1.11 Adult Congenital Heart Disease & Coarctation of the Aorta 1.12 Syncope: Reflex, Orthostatic & Cardiac Causes 1.13 Cardiac Physical Examination, Murmurs & Antithrombotic Selection
3 Chapter 2: Endocrinology, Diabetes & Metabolism (9% of Exam)
2.1 Diabetes Mellitus: Diagnosis, Glycemic Targets & Pharmacotherapy 2.2 Insulin Therapy, Hyperglycemic Emergencies & Chronic Complications 2.3 Thyroid Function Testing & Hypothyroidism 2.4 Thyrotoxicosis, Thyroid Storm & Thyroid Nodules 2.5 Adrenal & Pituitary Disorders 2.6 Hypercalcemia, Hypocalcemia & Disorders of Mineral Metabolism 2.7 Osteoporosis & Paget Disease of Bone 2.8 Ovarian, Testicular & Reproductive Endocrine Disorders 2.9 Hypoglycemia, Endocrine Tumors, Polyglandular Syndromes & Severe Hypertriglyceridemia
4 Chapter 3: Gastroenterology & Hepatology (9% of Exam)
3.1 Esophageal Disease 3.2 Stomach & Duodenal Disease and Gastrointestinal Hemorrhage 3.3 Inflammatory Bowel Disease 3.4 Celiac Disease & Irritable Bowel Syndrome 3.5 Diverticular Disease & Colorectal Cancer Screening 3.6 Viral Hepatitis, Steatotic & Alcohol-Associated Liver Disease 3.7 Cirrhosis & the Complications of Portal Hypertension 3.8 Acute Pancreatitis 3.9 Chronic Pancreatitis & Biliary Tract Disease 3.10 Inherited, Autoimmune & Drug-Induced Liver Disease 3.11 Small Intestinal Disease, Ischemia & Gastrointestinal Complications of HIV
5 Chapter 4: Infectious Disease (9% of Exam)
4.1 Lower Respiratory Tract Infections & Sepsis Syndromes 4.2 Viral Respiratory Pathogens & Tuberculosis 4.3 Central Nervous System Infections 4.4 Skin, Soft Tissue, Bone & Joint Infections 4.5 Infective Endocarditis & Cardiovascular Infection 4.6 Clostridioides difficile & Catheter-Related Bloodstream Infection 4.7 HIV Diagnosis, Antiretroviral Therapy & Prevention 4.8 Opportunistic Infections & Sexually Transmitted Infections 4.9 Fever of Unknown Origin, Neutropenic Fever & Toxic Shock 4.10 Travel-Related Illness, Vector-Borne Disease & Outbreaks 4.11 Infection Prevention, Nosocomial Infection & Postexposure Prophylaxis 4.12 Rheumatic Fever, Poststreptococcal Disease, Enteric & Hepatic Infections
6 Chapter 5: Pulmonary Disease (9% of Exam)
5.1 COPD: Diagnosis, GOLD Classification & Initial Pharmacotherapy 5.2 Interventions That Reduce COPD Mortality & Exacerbation Management 5.3 Asthma: Diagnosis, Stepwise Therapy & Status Asthmaticus 5.4 Interstitial Lung Disease & Idiopathic Pulmonary Fibrosis 5.5 Sarcoidosis, Hypersensitivity Pneumonitis & Occupational Lung Disease 5.6 Pulmonary Embolism: Diagnosis, Risk Stratification & Anticoagulation 5.7 Pulmonary Hypertension & Sleep-Disordered Breathing 5.8 Acute Respiratory Distress Syndrome & Mechanical Ventilation 5.9 Pleural Disease, Empyema & Pneumothorax 5.10 Bronchiectasis, Cystic Fibrosis & Restrictive Lung Disease 5.11 Evaluation of Cough, Dyspnea, Hemoptysis & the Solitary Pulmonary Nodule
7 Chapter 6: Rheumatology & Orthopedics (9% of Exam)
6.1 Rheumatoid Arthritis: Diagnosis & Systemic Manifestations 6.2 Antirheumatic Pharmacotherapy & the Spondyloarthropathies 6.3 Gout: Pathophysiology & Acute Management 6.4 Urate-Lowering Therapy & Calcium Pyrophosphate Deposition Disease 6.5 Osteoarthritis 6.6 Systemic Lupus Erythematosus 6.7 Systemic Sclerosis, Sjogren Syndrome & Inflammatory Myopathies 6.8 The Vasculitides 6.9 Regional Musculoskeletal Syndromes, Back Pain & Sports Injuries 6.10 Other Primary Rheumatic Disorders & Mixed Connective Tissue Disease 6.11 Osteonecrosis & Metabolic Bone Disease
8 Chapter 7: Hematology (6% of Exam)
7.1 Approach to Anemia & the Microcytic Anemias 7.2 Macrocytic, Normocytic & Hemolytic Anemias 7.3 Hemoglobinopathies, Thalassemias & Paroxysmal Nocturnal Hemoglobinuria 7.4 Platelet Disorders, Thrombocytopenia & the Bleeding Patient 7.5 Coagulation Factor Disorders, Thrombophilia & Anticoagulant Reversal 7.6 Acute Leukemias, Chronic Leukemias & Myeloproliferative Neoplasms 7.7 Lymphomas & Plasma Cell Disorders 7.8 Myelodysplastic Syndrome, Myeloproliferative Neoplasms & Porphyria 7.9 Transfusion Medicine & Late Complications of Transplantation
9 Chapter 8: Medical Oncology (6% of Exam)
8.1 Breast, Lung, Colorectal & Prostate Cancer 8.2 Oncologic Emergencies 8.3 Genitourinary & Gynecologic Malignancies 8.4 Head and Neck, Bone & Soft Tissue Cancer and Cancer of Unknown Primary 8.5 Complications of Cancer & Its Treatment 8.6 Cancer Prevention, Survivorship & Psychosocial Care
10 Chapter 9: Nephrology & Urology (6% of Exam)
9.1 Acute Kidney Injury: Staging, Etiology & Urine Microscopy 9.2 Glomerular Disorders & Nephrotic Syndrome 9.3 Nephritic Syndromes, RPGN & Indications for Renal Replacement Therapy 9.4 Chronic Kidney Disease: Staging & Progression Retardation 9.5 Complications of Chronic Kidney Disease: Anemia, CKD-MBD & Acidosis 9.6 Hyponatremia, Hypernatremia & Water Balance 9.7 Potassium Disorders & Systematic Acid-Base Analysis 9.8 Renal Tubular Acidosis & Nephrolithiasis 9.9 Prostate Disorders, Urinary Incontinence & Other Urologic Conditions 9.10 Cystic Kidney Disease, Obstructive Uropathy, Tubulointerstitial Disease & Hematuria
11 Chapter 10: Neurology (4% of Exam)
10.1 Acute Ischemic Stroke: Syndromes & Reperfusion 10.2 Transient Ischemic Attack, Secondary Prevention & Hemorrhagic Stroke 10.3 Headache & Facial Pain 10.4 Seizures, Epilepsy & Movement Disorders 10.5 Multiple Sclerosis & Neuromuscular Junction Disorders 10.6 Motor Neuron Disease & Acute Peripheral Neuropathy 10.7 Cranial Neuropathies & Neuro-Ophthalmology 10.8 Peripheral Neuropathies, CNS Tumors & Other Neurologic Disorders
12 Chapter 11: Psychiatry & Behavioral Health (4% of Exam)
11.1 Major Depressive Disorder & Medical Mimics 11.2 Antidepressant Pharmacotherapy & Treatment-Resistant Depression 11.3 Bipolar Disorder, Mood Stabilizers & Lithium Toxicity 11.4 Anxiety, Stress-Related & Obsessive-Compulsive Disorders 11.5 Alcohol Use Disorder & Withdrawal 11.6 Pharmacotherapy for Alcohol & Opioid Use Disorder 11.7 Toxidromes, Psychiatric Emergencies & Suicide Risk Assessment 11.8 Psychotic, Somatic Symptom, Factitious & Personality Disorders 11.9 Eating Disorders, Sleep Disorders & Sexual Health
13 Chapter 12: Dermatology (3% of Exam)
12.1 Dermatitis, Papulosquamous & Inflammatory Dermatoses 12.2 Acne, Rosacea & Cutaneous Infections 12.3 Herpes Zoster & Autoimmune Blistering Diseases 12.4 Nodules, Tumors & Cutaneous Oncology 12.5 Dermatologic Emergencies & Severe Cutaneous Adverse Reactions 12.6 Pigment Disorders, Alopecia, Nail Disease & Photosensitivity 12.7 Vascular Dermatoses, Environmental Injury & Cutaneous Signs of Systemic Disease
14 Chapter 13: Obstetrics & Gynecology / Women's Health (3% of Exam)
13.1 Contraception, Preconception Care & Teratogenicity 13.2 Hypertensive Disorders of Pregnancy & Gestational Diabetes 13.3 Thyroid Disease & Venous Thromboembolism in Pregnancy 13.4 Menopause & Menopausal Hormone Therapy 13.5 Abnormal Uterine Bleeding, Endometrial Disease & Gynecologic Cancer Screening 13.6 Breast Disorders & Diseases of the Vulva and Vagina 13.7 Menstrual Disorders, Fibroids, Endometriosis & Early Pregnancy Complications
15 Chapter 14: Geriatric Syndromes (3% of Exam)
14.1 Comprehensive Geriatric Assessment & Frailty 14.2 Falls, Gait Assessment & Polypharmacy 14.3 Urinary Incontinence & Pressure Injuries in Older Adults 14.4 Mild Cognitive Impairment, Dementia & Its Subtypes 14.5 Delirium & the Pharmacotherapy of Cognitive Disorders 14.6 Palliative Care, Hospice & Advance Care Planning 14.7 Chronic Wounds, Nutrition, Swallowing, Constipation & Hip Fracture 14.8 Sensory Impairment, Dizziness, Elder Mistreatment & Care Settings
16 Chapter 15: Allergy & Immunology (2% of Exam)
15.1 Anaphylaxis: Recognition & Emergency Management 15.2 Urticaria & Angioedema 15.3 Drug Allergy, Desensitization & Adult Immunodeficiency 15.4 Food Allergy, Insect Venom Hypersensitivity, Serum Sickness & Contrast Reactions 15.5 Rhinitis, Conjunctivitis, Eosinophilic & Mast Cell Disorders
17 Chapter 16: Preventive Medicine, Immunization & Clinical Epidemiology
16.1 The USPSTF Framework & Evidence-Based Cancer Screening 16.2 Cardiovascular & Metabolic Screening and Primary Prevention 16.3 Adult Immunization & Vaccines in Special Populations 16.4 Clinical Epidemiology, Biostatistics & Study Design
18 Chapter 17: Miscellaneous - Ethics, Patient Safety & Quality Improvement (2% of Exam)
17.1 Principles of Bioethics & Decisional Capacity 17.2 Informed Consent, Treatment Refusal & Special Scenarios 17.3 Surrogate Decision-Making, Advance Directives & Confidentiality 17.4 Patient Safety Science, Medical Error & Diagnostic Reasoning 17.5 Quality Improvement Methods, Health Disparities & Health Equity
19 Chapter 18: Perioperative Medicine & Medical Consultation
18.1 Preoperative Cardiovascular Risk Assessment 18.2 Preoperative Pulmonary Risk & Perioperative Medication Management 18.3 Perioperative Anticoagulation, Bridging & Postoperative Complications
20 Chapter 19: Ophthalmology (1% of Exam)
19.1 The Acute Red Eye & Ophthalmic Emergencies 19.2 Painless Vision Loss & Chronic Ophthalmic Disease 19.3 Uveitis, Scleritis & Orbital Disease
21 Chapter 20: Otolaryngology & Dental Medicine (1% of Exam)
20.1 Dizziness, Vertigo & Epistaxis 20.2 Ear Disorders, Hearing Loss & Upper Respiratory Infections 20.3 Oral Cavity, Salivary Gland, Laryngeal & Taste and Smell Disorders
10.6 Motor Neuron Disease & Acute Peripheral Neuropathy
Key Takeaways Explain This Topic AI
Motor neuron disease is enumerated under other neurologic disorders, and Guillain-Barre syndrome under peripheral neuropathy.
Amyotrophic lateral sclerosis combines upper and lower motor neuron findings without sensory loss or sphincter involvement.
Guillain-Barre syndrome produces ascending weakness with areflexia and albuminocytologic dissociation in the cerebrospinal fluid.
Plasma exchange and intravenous immunoglobulin are equally effective in Guillain-Barre syndrome, and corticosteroids are ineffective.
Serial forced vital capacity and negative inspiratory force detect neuromuscular respiratory failure before arterial blood gases become abnormal.
Last updated: August 2026
1. Motor Neuron Disease: Amyotrophic Lateral Sclerosis (ALS)
Amyotrophic lateral sclerosis (ALS / Lou Gehrig disease) is a fatal, progressive neurodegenerative disorder characterized by selective degeneration of both upper motor neurons (UMNs) in the primary motor cortex / corticospinal tract and lower motor neurons (LMNs) in the brainstem motor nuclei and anterior horns of the spinal cord.
Clinical Hallmark: Combined UMN and LMN Signs
Diagnosis requires the objective coexistence of UMN and LMN signs within the same body region / segment (bulbar, cervical, thoracic, or lumbosacral):
Upper Motor Neuron Signs: Spasticity, hyperreflexia, clonus, extensor plantar response ( positive Babinski sign ), pseudobulbar affect (inappropriate, involuntary laughing or crying episodes), and brisk preserved deep tendon reflexes in an otherwise severely atrophic, wasted limb.
Lower Motor Neuron Signs: Flaccid weakness, muscle atrophy, prominent fasciculations (visible twitching in tongue, arms, and legs), foot drop, hand intrinsic muscle wasting (preferential thenar wasting = "split-hand sign" ), and muscle cramps.
Systemic Sparing (What is NOT Affected in ALS):
Sensory function is completely normal (no numbness, paresthesias, or sensory loss).
Bowel and bladder sphincter control is preserved (Onuf's nucleus in S2-S4 is spared).
Extraocular eye movements are preserved (cranial nerves III, IV, VI spared).
Autonomic function is normal.
Diagnostic & Electrodiagnostic Workup
Electromyography and Nerve Conduction Studies (EMG/NCS): Demonstrates widespread active denervation (fibrillation potentials, positive sharp waves, fasciculation potentials) and chronic reinnervation (giant, polyphasic, long-duration motor unit action potentials [MUAPs]) across >=3 body segments.
Spine & Brain MRI: Essential to exclude compressive cervical spondylotic myelopathy, multiple sclerosis, or spinal cord tumors.
Evidence-Based Management of ALS
Disease-Modifying Pharmacotherapies:
Riluzole (50 mg PO BID): Glutamate antagonist that blocks voltage-gated sodium channels and inhibits glutamate release, reducing excitotoxicity. Prolongs survival or time to tracheostomy by 2 to 3 months ; monitor liver enzymes (ALT/AST).
Edaravone (Radicava): Free radical scavenger that reduces oxidative stress; slows functional motor decline in early-stage disease.
Multidisciplinary Supportive Interventions:
Non-Invasive Positive Pressure Ventilation (NIV / BiPAP): Indicated when Forced Vital Capacity (FVC) falls <50% of predicted or symptoms of nocturnal hypoventilation develop. Significantly prolongs survival and improves quality of life.
Percutaneous Endoscopic Gastrostomy (PEG) Tube: Indicated for severe dysphagia, choking, and progressive weight loss; should be placed before FVC drops <50% to avoid acute procedural respiratory failure.
Pseudobulbar Affect: Treated with Dextromethorphan-Quinidine (Nuedexta) .
- 2. Peripheral Neuropathies: Guillain-Barré Syndrome & Polyneuropathies
- 1. Guillain-Barré Syndrome (GBS / AIDP)
Pathophysiology: Acute post-infectious autoimmune polyradiculoneuropathy driven by molecular mimicry between microbial antigens (lipooligosaccharides) and host gangliosides on peripheral nerve axolemma and Schwann cells. Triggered by Campylobacter jejuni (>30% of cases; associated with severe axonal AMAN variant), Cytomegalovirus (CMV), Epstein-Barr virus (EBV), Mycoplasma pneumoniae , Zika virus, or SARS-CoV-2.
Clinical Presentation:
Rapidly progressive, symmetrical, ascending flaccid weakness beginning in the lower extremities and ascending over days to involve the arms, trunk, and cranial nerves (facial diplegia in 50%).
Hyporeflexia or complete Areflexia in affected limbs is mandatory for diagnosis.
Autonomic Instability (Dysautonomia in 65%): Blood pressure lability (severe hypertension or orthostatic hypotension), cardiac arrhythmias (sinus tachycardia, severe bradycardia, asystole), ileus, and urinary retention. Mandates continuous cardiac telemetry in an ICU/step-down setting.
Diagnostic Evaluation:
Lumbar Puncture (CSF Analysis): Classic Albuminocytologic Dissociation — markedly elevated CSF protein (>45 to 200+ mg/dL) with a normal CSF white blood cell count (<5 to 10 cells/mcL) . (Note: CSF protein may be normal during the first 3-5 days; repeat LP if suspicion is high).
Pulmonary Mechanics Monitoring: Serial bedside FVC (<15-20 mL/kg) and NIF (worse than -20 to -30 cm H2O) monitoring every 2-4 hours to guide elective intubation before hypoxemic collapse.
Disease-Modifying Treatment:
Intravenous Immunoglobulin (IVIG: 0.4 g/kg/day for 5 days [total 2.0 g/kg]) OR Plasma Exchange (PEX: 4-5 sessions over 7-14 days) .
Both modalities are equally effective. Combination of IVIG + PEX offers no synergistic benefit.
CRITICAL BOARD CONTRAINDICATION: Corticosteroids (systemic steroids) are INEFFECTIVE and may worsen long-term recovery; they must NEVER be administered in Guillain-Barré Syndrome .
2. Diabetic Distal Symmetric Polyneuropathy (DSPN) vs Mononeuritis Multiplex
Neuropathy Type Clinical Pattern & Pathophysiology Etiologies & Associations Diagnostic Workup & First-Line Management
Diabetic Distal Symmetric Polyneuropathy (DSPN) Length-dependent, symmetric "stocking-glove" sensory loss; burning neuropathic pain, hyperalgesia, loss of vibratory sense (128 Hz tuning fork) and loss of 10-g monofilament sensation; absent ankle reflexes Chronic hyperglycemia causing microvascular endoneurial ischemia, sorbitol accumulation, and advanced glycation end-products First-Line Pharmacotherapy for Pain: ; 1. Duloxetine (SNRI: 60 mg daily); 2. Pregabalin (alpha-2-delta calcium channel ligand: 150-300 mg daily); 3. Gabapentin (300-1800 mg daily); TCAs (Amitriptyline) are alternative; strict glycemic control
Mononeuritis Multiplex Painful, asymmetric, asynchronous involvement of >=2 non-contiguous peripheral nerves (e.g., right wrist drop [radial] + left foot drop [peroneal]) secondary to ischemic infarction of the vasa nervorum Systemic Necrotizing Vasculitides (Polyarteritis Nodosa [PAN], Granulomatosis with Polyangiitis [GPA], EGPA / Churg-Strauss), Cryoglobulinemia (HCV), SLE, RA, Diabetes (diabetic amyotrophy) Comprehensive vasculitis serology (ANCA, ANA, Cryoglobulins, RF, ESR/CRP, HBV/HCV); Combined Sural Nerve & Muscle Biopsy demonstrating necrotizing vasculitis.; Treatment: High-dose IV Corticosteroids + Cyclophosphamide or Rituximab