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Neurology Short Answers

1. Transcranial Doppler (TCD)

Definition: TCD is a non-invasive ultrasound technique that uses a pulsed Doppler transducer (2 MHz) to interrogate blood flow velocity through the basal intracranial arteries (typically the middle cerebral artery — MCA) through thin "acoustic windows" in the skull (temporal, orbital, foramen magnum).

Principle: Measures flow velocity (cm/s), not absolute flow. Changes in velocity reflect changes in vessel diameter or flow. Emboli produce characteristic high-intensity transient signals (HITS).

Clinical Applications in Neurology:

Vasospasm after subarachnoid hemorrhage: Elevated MCA velocity >120 cm/s indicates vasospasm; >200 cm/s indicates severe spasm. Daily monitoring guides clinical management.
Sickle cell disease: TCD screening identifies children at high risk for stroke (MCA velocity >200 cm/s); prophylactic transfusions reduce stroke risk by ~90%.
Intracranial stenosis / occlusion: Identifies large vessel occlusion in acute ischemic stroke.
Cerebral autoregulation assessment: Evaluates pressure-flow relationship in TBI patients.
Right-to-left shunt / Patent foramen ovale (PFO) detection: Bubble study — saline microbubbles detected in MCA following Valsalva indicate right-to-left shunt.
Brain death confirmation: Absent or reverberant flow (alternating systolic spikes with diastolic reversal) is a confirmatory ancillary test.
Microemboli detection: Solid vs. gaseous microemboli in cardiac surgery, carotid endarterectomy, and atrial fibrillation.

Limitations: User-dependent; requires an adequate temporal window (absent in ~10–20% of patients, especially older women); gives velocity not volume flow; cannot distinguish gaseous from solid emboli reliably.

— Bradley and Daroff's Neurology in Clinical Practice; Miller's Anesthesia 10e

2. Parkinson Plus Syndromes

Definition: A group of neurodegenerative disorders that share features of Parkinson's disease (bradykinesia, rigidity) but have additional clinical features, poor levodopa response, and a worse prognosis.

Major Parkinson Plus Syndromes:

Syndrome	Key Features	Pathology
Progressive Supranuclear Palsy (PSP)	Vertical gaze palsy (especially downgaze), axial rigidity > limb rigidity, early falls, frontal dementia	Tau deposits (4R tau)
Multiple System Atrophy (MSA)	Autonomic failure (OH, bladder), cerebellar ataxia (MSA-C) or Parkinsonism (MSA-P), no dementia	α-synuclein (GCIs)
Corticobasal Degeneration (CBD)	Apraxia, alien limb phenomenon, asymmetric rigidity, cortical sensory loss	Tau deposits
Dementia with Lewy Bodies (DLB)	Fluctuating cognition, well-formed visual hallucinations, REM sleep disorder, Parkinsonism	α-synuclein (Lewy bodies)

Key distinguishing features from PD:

Poor/absent sustained levodopa response
Early postural instability and falls (PSP)
Symmetric onset
Autonomic failure early (MSA)
Dementia precedes or concurrent with motor signs (DLB)

Cognitive profile: In PD with dementia (PDD), cognitive symptoms develop ≥2 years after motor onset, whereas in DLB they precede or occur within 1 year of motor signs. Both PDD and DLB show executive dysfunction, visuospatial deficits, and adverse reactions to antipsychotics.

— Bradley and Daroff's Neurology in Clinical Practice

3. Young Stroke

Definition: Stroke occurring in patients aged 15–45 years (some definitions extend to 55 years). Accounts for ~10–15% of all strokes.

Causes (differ from elderly stroke):

Cardiac causes:

Patent foramen ovale (PFO) with paradoxical embolism
Cardiomyopathy, valvular disease (mitral valve prolapse)
Atrial fibrillation (rheumatic, post-viral)
Infective endocarditis

Hematological:

Antiphospholipid antibody syndrome (APAS) — most important in young women
Sickle cell disease
Polycythemia, thrombocytosis
Protein C, Protein S, Antithrombin III deficiency
Factor V Leiden mutation

Vascular:

Cervical artery dissection (carotid/vertebral) — often after trauma, neck manipulation
Fibromuscular dysplasia
Vasculitis (CNS vasculitis, SLE, polyarteritis nodosa)
Moyamoya disease
Migraine with aura (especially with OCP use)

Metabolic/Genetic:

CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy)
MELAS (mitochondrial encephalopathy)
Homocystinuria, Fabry disease

Other:

Drug abuse (cocaine, amphetamines)
Oral contraceptive pills (combined with smoking/migraine)
Pregnancy and puerperium (CVST)

Investigation: MRI brain + DWI, MRA/CTA, echo with bubble study, hypercoagulability screen, APAS, cervical vessel imaging, CBC, lipids, HbA1c, urine drug screen, genetic screen if indicated.

— Bradley and Daroff's Neurology in Clinical Practice

4. Coma Mimics

Definition: Conditions that superficially resemble coma (unresponsiveness) but are not true disorders of consciousness.

Important Coma Mimics:

Locked-in Syndrome
- Bilateral pontine lesion (basilar artery occlusion, central pontine myelinolysis)
- Complete quadriplegia and anarthria with intact consciousness
- Preserved vertical eye movements and blinking — key differentiator
- EEG normal (waking pattern)
Psychogenic Unresponsiveness (Functional/Dissociative)
- May be associated with psychiatric illness or conversion disorder
- Eyelids resist passive opening; eyes deviate toward floor when tilted; optokinetic nystagmus present; EEG normal; pupils reactive
Akinetic Mutism
- Bilateral frontal or cingulate lesions
- Patient appears awake (eyes open, sleep-wake cycles) but makes no spontaneous movement or speech
- Different from coma — brainstem reflexes intact
Severe Metabolic Encephalopathy (not truly a mimic but must be excluded — drug intoxication, hepatic encephalopathy — correctable causes)
Abulia — marked reduction of voluntary action, speech, and emotion; eyes open; partial variant of akinetic mutism
Catatonia — psychiatric; waxy flexibility, posturing; responds to benzodiazepines

Key assessment: EEG (locked-in = normal waking; coma = delta waves), eye movements (preserved vertical gaze in locked-in), caloric testing, response to noxious stimuli.

— Plum and Posner's Diagnosis and Treatment of Stupor and Coma

5. Neurocysticercosis (NCC)

Definition: Infection of the human CNS by the larval stage of the pork tapeworm Taenia solium. The most common parasitic disease of the CNS worldwide and the most common cause of symptomatic epilepsy globally.

Epidemiology: Endemic in Latin America, sub-Saharan Africa, and Asia. Human becomes an accidental intermediate host by ingesting T. solium eggs (fecal-oral route from a human tapeworm carrier — autoinfestation or heteroinfection).

Pathology & Stages of Cysticerci:

Vesicular stage — live larva, minimal inflammation, often asymptomatic
Colloidal stage — larva begins to degenerate, significant perilesional edema
Granular-nodular stage — larva dies, calcification begins
Calcified stage — calcified granuloma, ongoing epileptogenesis

Clinical Features:

Seizures (most common — 70–90%): often partial with secondary generalization
Raised ICP: intraventricular or racemose NCC causing obstructive hydrocephalus
Focal neurological deficits
Meningitis: basilar meningitis from subarachnoid NCC
Encephalitis: in heavily infected patients (especially children)

Diagnosis:

Neuroimaging: CT (calcifications, ring-enhancing lesions); MRI (better for posterior fossa, live cysts — scolex visible as "hole with dot" sign)
Serology: EITB (enzyme-linked immunoelectrotransfer blot) — 98% sensitive with ≥2 cysts
Del Brutto diagnostic criteria (definitive, probable, possible)

Treatment:

Seizures: Antiepileptic drugs (AEDs)
Antiparasitic therapy: Albendazole 15 mg/kg/day (preferred) or Praziquantel 50–100 mg/kg/day — given with steroids to reduce inflammatory reaction
Corticosteroids: Dexamethasone/prednisone to reduce perilesional edema
Hydrocephalus: Ventriculoperitoneal shunt; endoscopic removal of intraventricular cysts

— Bradley and Daroff's Neurology in Clinical Practice

6. Mechanical Thrombectomy in Stroke

Definition: Endovascular catheter-based clot retrieval for acute ischemic stroke due to large vessel occlusion (LVO) of the proximal intracranial arteries.

Rationale: Narrow time window, limited recanalization, and hemorrhage risk of IV t-PA prompted development of mechanical devices for rapid flow restoration with lower risk of distal embolization.

Devices (historical to current):

MERCI device: First FDA-approved (2004); helical nitinol wire retriever; 48% recanalization; 60% with adjuvant therapy
Penumbra system: Aspiration-based; large-bore catheter
Stent retrievers (Solitaire, Trevo): Current standard of care — highest recanalization rates (~70–90%)

Landmark Trials (2015 — "The Year of Thrombectomy"):

MR CLEAN, ESCAPE, EXTEND-IA, SWIFT PRIME, THRACE — all showed significant benefit of stent retriever thrombectomy over medical therapy alone
DAWN and DEFUSE-3 — extended window to 24 hours in selected patients using perfusion imaging (CT perfusion / MR perfusion)

Indications:

LVO (ICA, M1, M2, basilar artery)
NIHSS ≥6 (significant deficit)
ASPECTS ≥6 (adequate viable tissue)
Within 6 hours of onset (or up to 24 hours if penumbra mismatch criteria met)
Can be combined with IV t-PA (bridging therapy) if eligible

Outcomes: Successful recanalization (TICI 2b-3) is an independent predictor of functional independence (mRS ≤2) and reduced mortality at 90 days.

Complications: Symptomatic intracranial hemorrhage (~4–5%), vessel perforation, distal embolization, access-site hematoma.

— Bradley and Daroff's Neurology in Clinical Practice

7. Management of Status Epilepticus (SE)

Definition: SE = seizure lasting >5 minutes OR two or more seizures without full recovery of consciousness between them.

Emergency Management (time-based protocol):

Phase 1 — Stabilization (0–5 min):

ABC, high-flow oxygen, positioning to prevent aspiration
IV access + bloods: glucose, electrolytes, Ca²⁺, Mg²⁺, LFTs, RFTs, AED levels, toxicology
Treat hypoglycemia: IV dextrose (with thiamine IV if alcoholism suspected)
Monitor: vitals, pulse oximetry, EEG if available

Phase 2 — Initial Therapy (5–20 min) — Benzodiazepines (first-line):

Lorazepam 0.1 mg/kg IV (max 4 mg) — preferred
Diazepam 0.15–0.2 mg/kg IV OR 0.2–0.5 mg/kg PR
Midazolam 0.2 mg/kg IM (if no IV access) — equally effective as IV lorazepam
Repeat once after 5 minutes if no response
Terminates seizures in ~70% of cases

Phase 3 — Second-Line Agents (20–40 min) if benzodiazepines fail:

Fosphenytoin 20 mg PE/kg IV at 150 mg PE/min (preferred over phenytoin — water-soluble, less cardiotoxic, can give IM)
Levetiracetam 60 mg/kg IV (up to 4500 mg)
Valproate 40 mg/kg IV (avoid in liver disease, thrombocytopenia, metabolic disorders, pregnancy)
These three are equally effective per current evidence (ESETT trial)

Phase 4 — Refractory SE (>40–60 min) — ICU anesthesia:

Propofol infusion (has antiepileptic activity — preferred induction agent if intubating)
Midazolam infusion
Ketamine (evidence from case reports for super-refractory SE)
Phenobarbital 20 mg/kg IV
Continuous EEG monitoring mandatory
Target: burst-suppression or seizure cessation

Identify and treat underlying cause: Hyponatremia, hypoglycemia, CNS infection, NCSE, drug toxicity, autoimmune encephalitis.

— Rosen's Emergency Medicine; Bradley and Daroff's Neurology in Clinical Practice

8. Myasthenic Crisis

Definition: Life-threatening exacerbation of myasthenia gravis (MG) resulting in respiratory failure due to weakness of respiratory muscles (diaphragm, intercostals). Defined as requiring ventilatory support.

Precipitants (identifiable in most cases):

Infection (most common), aspiration pneumonia
Surgery (perioperative stress)
Medication changes: missed doses, new drugs (aminoglycosides, fluoroquinolones, beta-blockers, chloroquine, magnesium, neuromuscular blockers)
Inadequate immunosuppression
Pregnancy, emotional stress

Differentiation — Cholinergic Crisis vs. Myasthenic Crisis:

Feature	Myasthenic Crisis	Cholinergic Crisis
Cause	Insufficient cholinesterase inhibition	Overdose of ChEIs
Pupils	Normal/dilated	Miotic (pinpoint)
Secretions	Normal	Excessive (SLUDGE)
Muscle fasciculations	Absent	Present
Edrophonium test	Improves	Worsens

Management:

ICU admission — close monitoring of respiratory function
Serial NIF (Negative Inspiratory Force): NIF < −20 cmH₂O = indication for intubation
- "20-30-40 rule": NIF < −20, VC < 30 mL/kg, or PEF < 40 L/min → intubate
BiPAP (non-invasive ventilation) — may avoid intubation if no hypercapnia
Discontinue ChEIs once intubated — reduces secretions, eliminates cholinergic overdose possibility
Plasmapheresis (PLEX) — preferred treatment; faster onset; use 5 sessions over 10 days. Superior to IVIg for rapid respiratory improvement. Avoid in: hemodynamic instability, sepsis, coagulopathy, 1st trimester pregnancy
IVIg 2 g/kg over 5 days — equally effective as PLEX for stabilization; preferred when PLEX contraindicated
Treat precipitating cause
Resume ChEIs in low doses after extubation, titrate to optimal dose
Extubation criteria: NIF > −20 cmH₂O AND expiratory pressure > 35–40 cmH₂O

Anesthetic considerations: Avoid neuromuscular blockers or use sparingly; inhalational agents alone usually provide adequate relaxation; depolarizing agent dose requirement may be increased; nondepolarizing agents cause prolonged blockade.

— Bradley and Daroff's Neurology in Clinical Practice

9. Brain Death

Definition: Irreversible cessation of all functions of the entire brain, including the brainstem. Legally equivalent to death in most jurisdictions.

Prerequisites (must be met before testing):

Establish irreversible coma of known cause (structural: TBI, SAH, ICH, ischemic stroke with herniation, hypoxic-ischemic encephalopathy)
Exclude reversible causes: hypothermia (core temp must be >36°C), drug/toxin intoxication (no sedatives, no anesthetic agents), metabolic disorders (severe electrolyte disturbances)

Clinical Criteria (Table 10.2 — Plum & Posner):

A. Coma of established cause

B. Absent brainstem reflexes:

No pupillary response to light; pupils midposition 4–6 mm
No corneal reflex
No caloric vestibulo-ocular response (cold water irrigation — no eye movement)
No gag reflex
No cough to tracheal suctioning
Absent sucking/rooting reflexes

C. Apnea test:

Disconnect ventilator, provide 100% O₂ via catheter
No respiratory effort when PaCO₂ ≥60 mmHg (or 20 mmHg above baseline)

D. Observation intervals (by age):

Term to 2 months: 48 hours (+ 2 confirmatory tests)
2 months to 1 year: 24 hours (+ 1 confirmatory test)
1–18 years: 12 hours (confirmatory optional)
Adults (≥18 years): interval optional; single examination acceptable

Confirmatory Tests (ancillary — when clinical exam incomplete):

EEG: Electrocerebral silence
Four-vessel cerebral angiography: No intracranial filling beyond carotid siphon
Radionuclide brain scan (Tc-99m HMPAO): No cerebral perfusion ("hollow skull" sign)
TCD: Absent flow or reverberant pattern
CT/MR angiography

Common etiologies: Traumatic brain injury, aneurysmal SAH, intracerebral hemorrhage, ischemic stroke with herniation, hypoxic-ischemic encephalopathy, fulminant hepatic necrosis with cerebral edema.

— Plum and Posner's Diagnosis and Treatment of Stupor and Coma

10. Acute Transverse Myelitis (ATM)

Definition: An acute myelopathic process, presumably autoimmune in origin, causing bilateral inflammatory demyelination/injury across a segment of the spinal cord, resulting in motor, sensory, and autonomic dysfunction below the lesion.

Etiology:

Idiopathic (post-infectious — most common)
Multiple sclerosis (often incomplete TM, asymmetric, short segment)
Neuromyelitis optica spectrum disorder (NMOSD): AQP4-IgG positive; longitudinally extensive TM (>3 vertebral segments); severe and often incomplete recovery
MOG antibody disease (MOGAD)
Systemic autoimmune: SLE, Sjögren's syndrome, antiphospholipid syndrome
Infectious: VZV, HSV, EBV, CMV, HIV, HTLV-1, enterovirus (post-infectious or direct)
Paraneoplastic
Vascular: Anterior spinal artery occlusion (usually abrupt onset)

Clinical Features:

Bilateral motor deficit below lesion → flaccid paraplegia (early) → spastic paraplegia (late)
Sensory level (usually thoracic)
Autonomic dysfunction: urinary retention, fecal incontinence, sexual dysfunction
Lhermitte's sign in cervical lesions
Typically bilateral but may be asymmetric
Rapid progression over hours to days

Investigations:

MRI spine: T2 hyperintensity (central cord), cord enlargement, ± gadolinium enhancement; cervical and thoracic most common
MRI brain: Exclude MS plaques
CSF: Pleocytosis, elevated protein, oligoclonal bands (suggest MS)
Serology: AQP4-IgG, MOG-IgG, ANA, anti-dsDNA, APAS panel
VEPs: To detect subclinical optic neuritis (NMO)

Treatment:

Acute: High-dose IV methylprednisolone 1 g/day × 3–5 days
Severe/refractory: Plasma exchange (PLEX) 5–7 sessions
NMOSD attacks: Also consider rituximab, azathioprine, or mycophenolate for relapse prevention
Supportive: Bladder catheterization, DVT prophylaxis, physiotherapy, pressure area care

Prognosis: ~1/3 recover fully, ~1/3 partial recovery, ~1/3 poor recovery. Poor prognostic factors: rapid onset, complete motor deficit, NMO spectrum, late treatment.

— Bradley and Daroff's Neurology in Clinical Practice; Rosen's Emergency Medicine

What is pe/kg

PE/kg stands for Phenytoin Equivalents per kilogram.

It is a standardized unit used specifically for fosphenytoin dosing.

Why "Phenytoin Equivalents"?

Fosphenytoin is a prodrug of phenytoin. To avoid confusion between the two drugs' molecular weights and to simplify dosing, fosphenytoin doses are expressed in terms of the amount of phenytoin they will yield after conversion in the plasma.

1 mg PE of fosphenytoin = the amount of fosphenytoin that produces 1 mg of phenytoin
This means you dose fosphenytoin exactly as you would phenytoin — just using the PE unit

Clinical Example

In Status Epilepticus (second-line therapy):

Fosphenytoin 20 mg PE/kg IV at a rate of 150 mg PE/min

This means: give 20 mg of phenytoin-equivalent per kg of body weight.

For a 60 kg patient → 1200 mg PE of fosphenytoin

Why use fosphenytoin instead of phenytoin?

Feature	Phenytoin	Fosphenytoin
Solubility	Poorly water-soluble	Water-soluble
IV rate	Max 50 mg/min	Max 150 mg/min (3× faster)
IM route	Cannot give IM	Can give IM
Cardiotoxicity	Higher (propylene glycol)	Lower
Vein irritation	Significant (purple glove syndrome)	Minimal

The PE unit ensures clinicians don't have to recalculate doses when switching between the two drugs.

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