Study guide
24.4 Motor Neuron Disease, Acute Myopathies, Rhabdomyolysis, and CINM (03.O.3–6)
ABIM Neurocritical Care Subspecialty Certification Exam
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1 Introduction & Exam Overview
1.1 Current Exam Facts 1.2 Eligibility, Practice Pathway, and the IM Training Route 1.3 Format, Scoring, Pearson VUE, and Score Reports 1.4 How to Use This Independent Study Guide
2 ICU Neurologic Exam, Cerebral Physiology, and CSF
2.1 Neurological Examination in the ICU 2.2 Cerebral Physiology, ICP, CBF, and Autoregulation 2.3 CSF Physiology
3 Core Neuropharmacology
3.1 Osmotic Agents 3.2 Anti-Seizure Drugs 3.3 Anesthetics, Sedatives, Analgesia, and Paralytics 3.4 Antihypertensives, Vasopressors, and Inotropes
4 Reperfusion Drugs, Airway, and Ventilation
4.1 Thrombolytics, Anticoagulants, and Antiplatelets 4.2 Reversal of Anticoagulation After Acute Hemorrhage 4.3 Airway Management and Tracheostomy 4.4 Mechanical Ventilation
5 Hemodynamics and Shock
5.1 Hemodynamic Monitoring 5.2 IABP, Temporary VADs, LVAD, and ECMO 5.3 Diagnosis and Management of Shock
6 Nutrition, Temperature, and ICU Prophylaxis
6.1 Nutrition (01.J) 6.2 Temperature Control (01.K) 6.3 ICU Prophylaxis, Delirium, and Early Mobility (01.L)
7 General Trauma
7.1 Emergency Evaluation of Polytrauma, Chest, and Abdominal Trauma 7.2 Long-Bone Fractures and Fat Embolism 7.3 Burns, Electrical Injury, and Hanging/Strangulation
8 Pulmonary Critical Care
8.1 Pulmonary Physiology and ARDS (01.N.1–2) 8.2 PE, Pneumonia, and Pulmonary Edema (01.N.3, 7–8) 8.3 COPD, Asthma, PAH, and Bronchoscopy Basics (01.N.4–6, 9)
9 Cardiovascular Critical Care
9.1 Cardiovascular Physiology, Stress Cardiomyopathy, ACS, and Valves 9.2 Arrhythmias and Pacing 9.3 Acute Aortic Dissection and Cardiac Ultrasound
10 Renal and Infectious Disease
10.1 AKI, RRT, and Renal Drug Dosing 10.2 Acid-Base and Electrolyte Disorders 10.3 Severe Sepsis, Septic Shock, and Infective Endocarditis 10.4 Antimicrobial Use and Infection in the Immunosuppressed
11 Endocrine and Salt-Water Disorders
11.1 Pituitary Apoplexy, DI, and Panhypopituitarism (01.R.1–4) 11.2 SIADH and Cerebral Salt Wasting (01.R.5–6) 11.3 Thyrotoxicosis, Myxedema, Adrenal Crisis, and Dysglycemia (01.R.7–9)
12 Gastrointestinal Critical Care
12.1 GI Physiology, Acute Abdomen, Bleed, Ileus, and Perforation (01.S.1–5) 12.2 Mesenteric Ischemia and Abdominal Compartment Syndrome (01.S.6–7) 12.3 Fulminant Liver Failure, Cirrhosis Decompensation, and Hepatic Dosing (01.S.8–10)
13 Hematologic Disorders
13.1 Anemia, Transfusion, Thrombocytopenia, Coagulopathy, and DIC (01.T.1–4) 13.2 VTE in the Neuro ICU (01.T.5) 13.3 Chemo/Immune, SCT, CAR-T, Sickle Cell, and TMA (01.T.6–10)
14 Neuroimaging
14.1 CT of Brain and Spine 14.2 MRI and CT/MR Perfusion 14.3 Noninvasive Angiography and Catheter Angiography
15 EEG, EMG, and CSF Analysis
15.1 EEG, Standard and Processed (02.B) 15.2 Basic EMG Interpretation (02.G) 15.3 CSF Analysis (02.H)
16 ICP, TCD, and Multimodality Monitoring
16.1 ICP Monitoring (02.C) 16.2 Transcranial Doppler (02.D) 16.3 Brain-Tissue Oxygen and Multimodality Monitoring (02.E–F)
17 Brain Death and Bedside Procedures
17.1 Brain Death Prerequisites and Clinical Exam (02.I) 17.2 Apnea Testing and Ancillary Studies (02.I) 17.3 Vascular Access, Thoracic Echo, and Lung Ultrasound (02.J–L)
18 Coma, Anoxia, and Intracranial Hypertension
18.1 Coma and Other States of Altered Consciousness (03.A) 18.2 Global Anoxia-Ischemia and Post-Resuscitation Encephalopathy (03.A.1) 18.3 Toxidromes, ICU Delirium, and Hypertensive Encephalopathy (03.A.2–4) 18.4 Intracranial Hypertension as a Disease State (03.B)
19 Acute Ischemic Stroke
19.1 IV Reperfusion Therapy (03.C.3) 19.2 Mechanical Thrombectomy Windows and Imaging Selection (03.C.3) 19.3 Malignant Hemispheric Infarction and Basilar Artery Occlusion (03.C.1–2)
20 Intraparenchymal Hemorrhage
20.1 Intracerebral Hematoma (03.D.1) 20.2 Cerebellar Hematoma (03.D.2) 20.3 Intraventricular Hemorrhage (03.D.3)
21 SAH, CVST, and Spinal Cord Infarction
21.1 Aneurysmal Subarachnoid Hemorrhage (03.E.1) 21.2 Non-Aneurysmal SAH (03.E.2) 21.3 Cerebral Venous Sinus Thrombosis (03.F) 21.4 Spinal Cord Infarction (03.G)
22 Vascular Anomalies and Traumatic Brain Injury
22.1 Unruptured Aneurysm, Cavernoma, AVM, and Dural AVF (03.H) 22.2 Diffuse Axonal Injury and Cerebral Contusions (03.I.1–2) 22.3 Epidural Hematoma, Subdural Hematoma, and Penetrating Injury (03.I.3–4, 7) 22.4 Arterial Dissection and Carotid-Cavernous Fistula (03.I.5–6)
23 Spine, Hydrocephalus, and CNS Infection
23.1 Spinal Cord Injury, Central Cord, and Neurogenic Shock (03.J) 23.2 Unstable Spine Fractures (03.K) 23.3 Hydrocephalus and CSF Diversion (03.L) 23.4 Acute CNS Infections (03.M)
24 Seizures and Neuromuscular Emergencies
24.1 Status Epilepticus and Seizures (03.N) 24.2 Guillain-Barré Syndrome (03.O.1) 24.3 Myasthenic Crisis (03.O.2) 24.4 Motor Neuron Disease, Acute Myopathies, Rhabdomyolysis, and CINM (03.O.3–6)
25 Inflammatory Disease, Neuro-Oncology, and Special Populations
25.1 Fulminant Demyelinating Diseases (03.P) 25.2 Autoimmune Encephalitis and Acute Autonomic Hyperactivity (03.Q–R) 25.3 Neuro-Oncology and Treatment Complications (03.S) 25.4 Pregnancy/Post-Partum, Post-Transplant, and Pediatric Patients (03.T–U)
26 Neurosurgical and Perioperative Complications
26.1 Postoperative Seizures, Hemorrhage, Ischemia, and Hyperperfusion (04.A, C, D, H) 26.2 Infection, CSF Leak, and Pneumocephalus (04.B, E, F) 26.3 Complications of EVD and Lumbar Drain (04.G, I)
27 Ethics, Prognostication, and Organ Donation
27.1 Communication, Decision-Makers, Advance Directives, and DNR (05.A, B, G) 27.2 Uncertainties of Prognostication and the Self-Fulfilling Prophecy (05.C) 27.3 Palliative Care, Withdrawal, Withholding, and Futility (05.D–F) 27.4 Donation After Cardiac Death and Care of the Organ Donor (05.H–I)
24.4 Motor Neuron Disease, Acute Myopathies, Rhabdomyolysis, and CINM (03.O.3–6)
Key Takeaways Explain This Topic AI
Amyotrophic lateral sclerosis respiratory failure is treated first with noninvasive ventilation; tracheostomy is a goals-of-care decision rather than an automatic next procedure.
Inflammatory myopathy must be separated from toxic myopathy: statin immune-mediated necrotizing myopathy with anti-HMGCR antibodies continues after the statin is stopped and needs immunosuppression.
Rhabdomyolysis threatens hyperkalemia, acute kidney injury, and compartment syndrome; treat with isotonic fluids and follow creatine kinase, potassium, and urine output.
Critical illness neuromyopathy is flaccid quadriplegia after sepsis, corticosteroids, and neuromuscular blockade, presenting as wean failure; it is a diagnosis of exclusion supported by EMG.
Guillain-Barré syndrome, myasthenia, critical illness neuromyopathy, and spinal shock can all cause flaccid weakness; sensory level, extraocular fatigability, CSF protein, and timing in the ICU separate them.
Last updated: September 2026
Four problems that all look like a floppy ICU patient
Blueprint topics 03.O.3–6 sit together because the neuroICU is asked, almost daily, why a patient cannot wean. The answers are not interchangeable. Motor neuron disease is a progressive degenerative diagnosis with an advance-care conversation at its center. Acute myopathies are muscle-limited, often CK-rich, and split into immune versus toxic. Rhabdomyolysis is a medical emergency of potassium, kidney, and compartments. Critical illness neuromyopathy (CINM) is a diagnosis of exclusion after sepsis and ICU treatments. Mixing them produces either futile thymectomy talk or missed compartment syndrome.
Motor neuron disease and the ventilator
Amyotrophic lateral sclerosis (ALS) combines upper and lower motor neuron signs: brisk reflexes or a Babinski sign in a wasted, fasciculating limb is the classic mixed picture. Bulbar ALS presents with dysarthria, dysphagia, and poor cough. The ICU appearance is hypercapnic respiratory failure, aspiration pneumonia, or inability to wean after an unrelated intubation.
Respiratory support is stepwise and preference-sensitive:
Measure FVC , sniff nasal inspiratory pressure (SNIP) or NIF, and nocturnal oximetry or capnography. Symptoms of orthopnea, morning headache, and REM-related hypoventilation often precede daytime hypercapnia.
Noninvasive ventilation (NIV) , usually nocturnal bilevel positive airway pressure, is first-line when the patient wants respiratory support. It prolongs survival and improves symptoms in ALS with respiratory insufficiency.
Secretion management (mechanical insufflation–exsufflation, cough assist, suctioning, and sometimes a feeding tube) determines whether NIV can succeed.
Tracheostomy ventilation can extend life in patients who choose it. It is not an automatic escalation. The conversation covers communication, 24-hour care, and what the patient considers an acceptable life. Do not perform a midnight tracheostomy in a newly diagnosed patient who has never discussed goals.
Diaphragm pacing is not standard emergency care. Riluzole and edaravone are disease-modifying outpatient drugs, not ICU rescue.
The examination trap is labeling every wasted, areflexic, ventilator-dependent patient as ALS. ALS does not explode over 48 hours after septic shock; CINM does. ALS usually has mixed upper and lower signs and a history of months of twitching and falls. New ALS can present to the ICU, but it still needs a thoughtful diagnosis, not a reflex tracheostomy.
Acute myopathies: inflammatory versus toxic
Inflammatory myopathies (dermatomyositis, overlap/anti-synthetase disease, immune-mediated necrotizing myopathy) produce subacute proximal weakness, often with a CK in the thousands, and extra-muscular clues (rash, interstitial lung disease, arthritis). ICU issues are respiratory muscle weakness, aspiration, and myocarditis in selected antibodies (for example anti-MDA5 or anti-SRP). Treatment is immunotherapy after infection is addressed: corticosteroids, IVIG, rituximab, or other agents depending on the serotype.
Toxic myopathies start with a drug or alcohol history:
Toxin / syndrome Timing CK and antibodies What to do
Statin-associated immune-mediated necrotizing myopathy Continues or worsens after the statin is stopped CK often 2,000–20,000 IU/L; anti-HMGCR (or anti-SRP in non-statin IMNM) Stop the statin; this is not a wait-it-out toxic myopathy—immunosuppression (steroids, IVIG, rituximab) is usually required
Ordinary statin myalgia / self-limited necrotizing injury Improves after stopping the drug Mild-moderate CK, antibody-negative Stop statin, fluids if CK is high, do not rechallenge blindly
Alcohol -related necrotizing myopathy Binge or withdrawal Very high CK, rhabdomyolysis Fluids, electrolyte repletion, watch compartments
Colchicine, chloroquine, amiodarone Chronic Vacuolar myopathy; CK variable Stop the drug
ICU thick-filament myopathy After high-dose steroids and neuromuscular blockade CK normal or moderately high Supportive; overlaps CINM
Do not restart a statin in anti-HMGCR disease. Do not treat ordinary alcohol rhabdomyolysis with rituximab. The serology and the time course after toxin removal make the split.
Rhabdomyolysis
Rhabdomyolysis is skeletal muscle necrosis releasing myoglobin, potassium, phosphate, and organic acids. Triggers in the neuroICU include prolonged seizure, immobilization, compartment syndrome, neuroleptic malignant syndrome, malignant hyperthermia, cocaine or synthetic cannabinoids, trauma, and the toxic myopathies above.
Problem Why it kills Management
Hyperkalemia Ventricular arrhythmia, especially while still seizing or ischemic Calcium if ECG changes, insulin-glucose, beta-agonist, bicarbonate in selected acidosis, urgent dialysis if oliguric
Acute kidney injury Myoglobin precipitates in tubules; dipstick reads blood with few red cells Isotonic crystalloid to maintain urine output; avoid NSAIDs; dialysis for usual indications
Hypocalcemia / hyperphosphatemia Released phosphate binds calcium Do not chase mild hypocalcemia aggressively during the oliguric phase; it rebounds during recovery
Compartment syndrome Swollen muscle raises intra-compartment pressure Pain out of proportion, tense compartments, rising CK despite fluids; surgical fasciotomy, not more mannitol as a substitute
CK tracing Confirms the diagnosis and trajectory CK often >5 times the upper limit of normal and frequently in the tens of thousands; treat the complications, not a single CK number
Urine that dips positive for blood without red cells on microscopy is a classic myoglobin clue. Alkalinization is optional and secondary to volume. Never use succinylcholine if malignant hyperthermia or denervation is in play.
Critical illness neuromyopathy
ICU-acquired weakness after days of critical illness is usually critical illness polyneuropathy (CIP) , critical illness myopathy (CIM) , or both—together CINM . Typical story: septic shock, multi-organ failure, high-dose corticosteroids, and days of neuromuscular blockade. As the lungs improve, the patient is flaccid, areflexic or hyporeflexic, and cannot wean. Facial and extraocular muscles are usually spared . Sensation is reduced in CIP and relatively spared in pure CIM. Dysautonomia like GBS is not the dominant picture. CSF is normal.
CINM is a diagnosis of exclusion . Before you accept it, rule out residual neuromuscular blockade (train-of-four), occult cervical cord injury, ongoing sedative accumulation, GBS that was the reason for admission, myasthenic crisis, hypophosphatemia, severe hypokalemia, and untreated status epilepticus.
Electrodiagnosis, when feasible:
CIM: low compound muscle action potential (CMAP) amplitudes, prolonged CMAP duration , relatively preserved sensory nerve action potentials (SNAPs), myopathic recruitment. Direct muscle stimulation shows inexcitable muscle.
CIP: axonal sensorimotor pattern with low SNAPs and CMAPs, relatively preserved conduction velocities (not GBS demyelination).
Biopsy, rarely needed, may show myosin thick-filament loss.
There is no IVIG indication for CINM. Treatment is supportive: stop unnecessary steroids and paralytics, treat sepsis, glycemic control, early mobilization, and time. Recovery is weeks to months; CIP recovers more slowly than CIM. Face-sparing flaccid quadriplegia after a septic week is CINM until a better diagnosis is proven—not a reason to start a GBS steroid-free IVIG course without examining the timeline.
Distinguishing GBS, MG, CINM, and spinal shock
Feature GBS Myasthenic crisis CINM Spinal shock
Timing Days after infection, community onset Known MG or subacute fatigable illness; crisis over hours–days After days of ICU sepsis, steroids, neuromuscular blockade Immediate after spinal cord injury
Pattern Ascending, relatively symmetric Fatigable; ocular and bulbar prominent Flaccid quadriplegia, face usually spared , proximal plus respiratory Sensory and motor level ; arms spared in thoracic lesions
- Reflexes Absent Normal or reduced Reduced Absent below the lesion
- Sensory Distal loss common No primary sensory loss CIP yes, CIM no Sensory level, often a truncal band
Autonomic Labile BP, arrhythmias, ileus Usually not GBS-like storms Not the GBS picture Neurogenic shock : hypotension with bradycardia , priapism
CSF High protein, few cells (may be delayed) Normal Normal Normal
EMG / extra Demyelinating or axonal neuropathy Decrement, jitter; normal nerve if not wasted Axonal CIP, inexcitable CIM, prolonged CMAP Normal nerve conduction acutely if the lesion is cord
Rescue IVIG or PLEX; no steroids IVIG or PLEX; steroids later Supportive; no IVIG Immobilize, MAP support (often ≥85 mm Hg for 7 days in acute traumatic SCI practice), not NASCIS-dose steroids as routine
Spinal shock is the temporary loss of all cord function below an acute lesion. It is not a peripheral neuropathy. A sensory level, a history of trauma or aortic surgery, priapism, and bradycardic hypotension send you to spine imaging, not to IVIG.
Examination traps
Tracheostomy on ALS hospital day 0 without a goals conversation.
Restarting a statin in anti-HMGCR necrotizing myopathy.
Treating CINM with IVIG because the patient is areflexic.
Calling spinal shock GBS because both are flaccid and areflexic.
Ignoring a tense calf in a patient whose CK will not fall.
Using succinylcholine in rhabdomyolysis, denervation, or suspected malignant hyperthermia.