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Bilateral Foot Drop — Causes

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1. Central / Upper Motor Neuron (Spinal Cord)

• Spastic paraparesis from myelopathy (cervical spondylosis, MS, transverse myelitis, tumor, AVM)
• Scissor gait / paraparetic gait with bilateral foot drop, extended knees, and adductor crossover

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2. Anterior Horn Cell (Lower Motor Neuron — Spinal)

• Amyotrophic lateral sclerosis (ALS) / Motor Neuron Disease — may begin distally and asymmetrically in the legs
• Progressive Spinal Muscular Atrophy (PSMA)
• Poliomyelitis

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3. Lumbosacral Roots

• Bilateral L4–L5 radiculopathy — disc disease, spinal stenosis, cauda equina lesion
• Lumbar plexopathy (bilateral, e.g., retroperitoneal disease)

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4. Peripheral Nerve (Polyneuropathy) — Most Common Cause

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5. Neuromuscular Junction

• Typically does not produce isolated foot drop

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6. Muscle (Myopathy)

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7. Other

• Dystonia — action dystonia of the foot can mimic foot drop
• Sensory ataxia (severe deafferentation, e.g., tabes dorsalis, subacute combined degeneration) — steppage gait with pseudo-foot drop due to proprioceptive loss

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Key Distinguishing Points

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• Adams and Victor's Principles of Neurology, 12th Ed. — Steppage gait, distal bilateral limb palsies
• Bradley and Daroff's Neurology in Clinical Practice — Box 25.2: Causes of Foot Drop
• Localization in Clinical Neurology, 8th Ed. — Steppage gait, bilateral foot drop
• Adams and Victor's Principles of Neurology, 12th Ed. — Distal muscular dystrophies, scapuloperoneal dystrophy

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Wrist Drop — Causes

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1. Radial Nerve Palsy — By Site of Lesion (Most Common Overall Cause)

A. Axillary (High) Radial Nerve Lesion

Triceps is affected here because branches to triceps arise proximal to the spiral groove.

B. Spiral Groove (Mid-Humeral) Lesion — Most Common Site

C. Posterior Interosseous Nerve (PIN) Entrapment — Distal to Elbow

• Entrapment in the radial tunnel (at the arcade of Frohse / supinator muscle)
• Trauma or dislocation of radial head
• Lipoma, ganglion, synovial cyst compressing the nerve
• Features: Finger drop (extensors of wrist and fingers weak) but no sensory loss and no true wrist drop — wrist extensors (extensor carpi radialis longus) are partially spared, so the wrist deviates radially on extension rather than fully dropping.

D. Distal / Superficial Radial Nerve Lesion

• Tight wristbands, handcuffs, IV catheter — sensory loss only (cheiralgia paresthetica), no wrist drop

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2. C7 Nerve Root Radiculopathy

• C6–C7 disc herniation — the most common cervical root involved
• Wrist drop + triceps weakness + triceps reflex loss + sensory loss over 2nd and 3rd digits
• Causes: cervical disc prolapse, cervical spondylosis, tumour, trauma

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3. Brachial Plexus (Posterior Cord / Middle Trunk)

• Posterior cord lesion of the brachial plexus — wrist drop + deltoid weakness (axillary nerve also from posterior cord)
• Erb-Duchenne palsy (C5–C6) — affects upper trunk; does NOT typically cause wrist drop
• Pancoast tumour (apical lung tumour) invading lower plexus — predominantly C8/T1 but can extend

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4. Cortical / Central (Rare)

• Cerebral cortical infarct in the "hand knob" area of the precentral gyrus can mimic wrist drop (pseudo-radial nerve palsy) — but the weakness is upper motor neuron (spastic, hyperreflexic, no sensory loss in radial distribution)

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5. Toxic / Systemic Causes (Bilateral Wrist Drop)

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6. Summary by Level

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• Harrison's Principles of Internal Medicine, 22nd Ed. — Radial neuropathy
• Neuroanatomy through Clinical Cases, 3rd Ed. — Radial neuropathy, upper extremity nerve injuries
• General Anatomy & Musculoskeletal System (THIEME Atlas) — Wrist drop; radial nerve lesion sites
• Bradley and Daroff's Neurology in Clinical Practice — Radial neuropathy; lead neuropathy
• Localization in Clinical Neurology, 8th Ed. — Pseudo-radial nerve palsy (cortical)
• Katzung's Basic & Clinical Pharmacology, 16th Ed. — Lead-induced wrist drop

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Wasting of the Small Muscles of the Hand — Differential Diagnosis

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Anatomical Framework

Cortex / UMN → Spinal cord (C8–T1) → Anterior horn cells
→ Nerve roots (C8, T1) → Lower trunk brachial plexus
→ Median + Ulnar nerves → Intrinsic hand muscles

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1. Peripheral Nerve

Ulnar Nerve Palsy

• Compression at elbow (cubital tunnel / ulnar groove) — most common cause of intrinsic wasting
• Compression at wrist (Guyon's canal) — hypothenar + interossei, sparing forearm muscles
• Chronic pressure from air hammers, prolonged leaning on elbow
• Wasting of hypothenar eminence, first dorsal interosseous, interossei → claw hand (4th & 5th fingers)
• Associated: sensory loss over 4th–5th fingers and ulnar border

Median Nerve Palsy

• Carpal tunnel syndrome — most common peripheral nerve entrapment; thenar wasting (LOAF muscles)
• Proximal median nerve compression (pronator teres, anterior interosseous nerve)
• Features: thenar (lateral) wasting; sensory loss over thumb/index/middle finger; positive Tinel/Phalen

Combined Ulnar + Median = Complete Intrinsic Wasting

• Both nerves injured → "all-intrinsic" wasting

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2. Brachial Plexus (Lower Trunk — C8, T1)

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3. Nerve Roots (C8–T1)

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4. Spinal Cord (C8–T1 Anterior Horn / Cord)

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5. Distal Myopathy / Muscle Disease

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6. Vasculitic / Multifocal Neuropathy

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Summary Table by Distribution

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• Adams and Victor's Principles of Neurology, 12th Ed. — Lower brachial plexus paralysis; thoracic outlet syndrome
• Bradley and Daroff's Neurology in Clinical Practice — Ulnar neuropathy; thoracic outlet; ALS
• Eric Kandel Principles of Neural Science, 6th Ed. — ALS and hand wasting
• Gray's Anatomy for Students — Cervical rib; intrinsic wasting
• Harrison's Principles of Internal Medicine, 22nd Ed. — Thoracic outlet syndrome
• Localization in Clinical Neurology, 8th Ed. — Cervical cord; syringomyelia

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Small Muscles of the Hand — Wasting: A Complete Viva Approach

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Step 1: Anatomy — What Are the Small Muscles of the Hand?

Viva key point: All intrinsic hand muscles are C8–T1. Any lesion affecting C8–T1 at any level can cause wasting.

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Step 2: Clinical Approach — History

A. Pattern of wasting

• Thenar only → median nerve (CTS) until proven otherwise
• Hypothenar + interossei → ulnar nerve
• All intrinsics, unilateral → C8/T1 root, lower trunk, or cord
• All intrinsics, bilateral → ALS, syringomyelia, bilateral entrapment, distal myopathy

B. Sensory symptoms

• Thumb/index/middle fingers, nocturnal → CTS (median)
• Ring/little finger, medial forearm → ulnar nerve / lower trunk
• Dissociated (pain/temp lost, touch preserved) → syringomyelia
• No sensory loss → anterior horn cell (ALS, PMA) or myopathy

C. Pain

• Neck pain + arm radiation → cervical radiculopathy/spondylosis
• Severe shoulder/arm pain at onset → Pancoast tumour, Parsonage-Turner
• Aching ulnar forearm → thoracic outlet syndrome
• Painless progressive → ALS, hereditary neuropathy (CMT), myopathy

D. Other features

• Fasciculations → anterior horn cell disease
• Horner syndrome (ptosis, miosis, anhidrosis) → C8/T1 lesion, Pancoast, syringomyelia
• Legs involved → consider cord lesion (ALS, spondylotic myelopathy, syringomyelia)
• Occupation/trauma → entrapment, repetitive stress
• Bilateral wrist + foot drop → lead neuropathy, CMT, myopathy

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Step 3: Clinical Examination Approach

General Inspection

• Thenar wasting → flat thenar eminence (CTS, median palsy, C6–C7 but also C8 root)
• Hypothenar + first dorsal interosseous wasting → ulnar palsy (characteristic "guttering")
• All intrinsics → generalised pitting on dorsum
• Claw hand → ulnar (4th/5th) or all fingers (combined median + ulnar)
• Fasciculations → ALS

Motor Testing

Reflexes

Absent finger flexor reflex = C8/T1 involvement at root or cord level

Sensory Testing

• Map carefully: median territory (lateral 3½ digits), ulnar (medial 1½), T1 inner forearm
• Test pain/temp separately from touch → if dissociated = syringomyelia

Look for Associated Signs

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Step 4: Localization Framework

Cortex → rarely (pseudoulnar palsy with parietal/precentral infarct)
        ↓
Cervical cord (C8–T1) → spondylotic myelopathy, syringomyelia,
                          ALS, intramedullary tumour
        ↓
Nerve roots (C8, T1) → disc prolapse, spondylosis, trauma
        ↓
Lower trunk / brachial plexus → Pancoast, cervical rib/TOS, Klumpke
        ↓
Peripheral nerve → ulnar (elbow/wrist), median (CTS), combined
        ↓
Neuromuscular junction → not a significant cause
        ↓
Muscle → IBM, distal dystrophy, myotonic dystrophy

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Step 5: Key Differentiating Features (High-Yield Viva)

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Step 6: Investigations

First-Line

Second-Line (Targeted)

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Step 7: Classic Viva Questions & Answers

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• Localization in Clinical Neurology, 8th Ed. — Split-hand; C8/T1 cord lesions; spondylotic myelopathy; TOS
• Adams and Victor's Principles of Neurology, 12th Ed. — Lower plexus paralysis; TOS; patterns of myopathic weakness
• Bradley and Daroff's Neurology in Clinical Practice — Radial/ulnar/median neuropathy; ALS split-hand; TOS electrodiagnostics
• Harrison's Principles of Internal Medicine, 22nd Ed. — TOS; nerve investigations
• Eric Kandel Principles of Neural Science, 6th Ed. — ALS and hand wasting

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Cherry-Red Spot — Complete Overview

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Definition & Mechanism

Key point: The fovea appears red in both cases for the same reason — it has no ganglion cells, so the choroidal blush is unobstructed; the surrounding retina is white/opaque due to ischaemia or storage material.

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Causes — Classified

1. Vascular (Acute — Unilateral)

• Emboli: cholesterol (Hollenhorst plaque — carotid atheromas), calcium (cardiac valves), platelet-fibrin
• Thrombosis: in situ; associated with carotid stenosis, GCA
• GCA (giant cell arteritis) — always exclude in >55 yr
• Cardiac embolism (AF, endocarditis, valvular disease)
• Hypercoagulable states, sickle cell disease

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2. Lysosomal Storage Diseases (Bilateral — Symmetric — Present in Infancy/Childhood)

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3. Toxic Causes

• Carbon monoxide poisoning
• Methanol poisoning
• Quinine toxicity
• Dapsone toxicity
• Gentamicin toxicity (intraocular)

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4. Trauma

• Commotio retinae (Berlin's oedema) — blunt ocular trauma; retinal whitening from photoreceptor outer segment fragmentation; cherry-red spot at posterior pole; usually resolves spontaneously but may mimic CRAO

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Key Distinguishing Points (Viva)

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Cherry-Red Spot Myoclonus Syndrome

• Progressive myoclonus (severe, incapacitating, intention myoclonus)
• Visual failure
• Cherry-red spot
• Autosomal recessive; sialidase (neuraminidase) deficiency
• Listed as a cause of myoclonic epilepsy

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Important Viva Mnemonics

• Tay-Sachs (GM2)
• ALS-like variants of hexosaminidase deficiency (adult)
• Niemann-Pick (A, B)
• Farber disease
• Mucolipidosis I / Sialidosis
• Sandhoff disease (GM2)

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• Kanski's Clinical Ophthalmology, 10th Ed. — Cherry-red spot at the macula; storage diseases
• Robbins, Cotran & Kumar Pathologic Basis of Disease — CRAO mechanism; Tay-Sachs; storage diseases
• Adams and Victor's Principles of Neurology, 12th Ed. — Diseases displaying cherry-red macular spot; sialidosis; Tay-Sachs; Sandhoff
• The Wills Eye Manual — Differential diagnosis of cherry-red spot; CRAO etiology
• Rosen's Emergency Medicine — CRAO clinical features

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Aseptic Meningitis — Complete Overview

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Definition

• Fever, headache, meningismus (neck stiffness, Kernig/Brudzinski signs)
• CSF pleocytosis — predominantly lymphocytic
• Normal CSF glucose (occasionally mildly reduced)
• Mildly elevated CSF protein
• Negative bacterial cultures

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CSF Profile in Aseptic vs. Bacterial Meningitis

Note: In early viral meningitis, neutrophils may predominate for the first 24–48 hours. Also, drug-induced meningitis (especially TMP-SMX) often causes neutrophilic CSF pleocytosis — an important trap.

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Causes — Classified

1. Viral (Most Common — 80%+)

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2. Bacterial (Atypical / Culture-negative)

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3. Non-Infectious — Systemic Disease

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4. Neoplastic (Carcinomatous/Lymphomatous Meningitis)

• Metastatic carcinoma (breast, lung, melanoma)
• CNS tumours: meningeal gliomatosis, dysgerminomas, ependymomas
• Epidermoid/dermoid cyst rupture (releases squamous cells + cholesterol crystals into CSF → chemical meningitis)
• Hypoglycorrhachia is the clue — low CSF glucose suggests neoplastic or granulomatous meningitis

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5. Drug-Induced Aseptic Meningitis (DIAM)

A hypersensitivity/idiosyncratic reaction, not dose-dependent; recurs with re-exposure.

A. NSAIDs (Most Common Drug Class)

Patients with SLE and connective tissue diseases have disproportionately higher risk of NSAID-induced meningitis.

B. Antimicrobials

C. Immunologics / Biologics

D. Other Drugs

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6. Chemical/Inflammatory (Non-Drug)

• Epidermoid/dermoid cyst rupture — cholesterol crystals, keratin in CSF
• Craniopharyngioma leakage
• Post-neurosurgical or post-LP chemical irritation
• Intrathecal contrast or drugs → arachnoiditis

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Mollaret's Meningitis (Recurrent Benign Lymphocytic Meningitis)

• HSV-2 is the primary cause (>80% of cases confirmed by CSF PCR)
• Recurrent self-limited episodes of headache, fever, meningismus over years
• Each attack lasts a few days and resolves spontaneously
• Classic CSF finding: Mollaret cells — large ghost-like endothelial/epithelioid cells (pathognomonic but transient)
• Drug-induced meningitis (NSAIDs, IVIG) can also recur with re-exposure and mimic this syndrome
• Also caused by: SLE, dermoid cyst leakage, Behçet's disease

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Key Viva Points

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• Adams and Victor's Principles of Neurology, 12th Ed. — Acute aseptic meningitis; causes; CSF findings
• Goldman-Cecil Medicine — Non-infectious causes of aseptic meningitis; drug hypersensitivity table
• Bradley and Daroff's Neurology in Clinical Practice — Recurrent meningitis; Mollaret's; NSAID-induced; IVIG
• Rosen's Emergency Medicine — NSAID-induced meningitis; ibuprofen
• Harrison's Principles of Internal Medicine, 22nd Ed. — Viral meningitis; CSF differentiation

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Causes of Optic Neuritis

Definition

• Pain on eye movement (~90%)
• Reduced visual acuity and colour vision (red desaturation)
• Relative Afferent Pupillary Defect (RAPD) — Marcus Gunn pupil
• Visual field defect (central/cecocentral scotoma most common)
• Disc swelling (papillitis) in ~1/3; normal disc (retrobulbar neuritis) in ~2/3
• Uhthoff's sign — worsening with heat/exercise (suggests demyelination)

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Classification: Typical vs. Atypical

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Causes — Classified

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1. Demyelinating Disease (Most Common in Adults — ~85% of Typical Cases)

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2. Infectious Causes

Viral

Bacterial

Fungal

Parasitic

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3. Autoimmune / Systemic Inflammatory Diseases

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4. Contiguous Spread / Local Inflammation

• Orbital cellulitis / abscess
• Sinusitis (especially ethmoid/sphenoid — posterior orbit)
• Meningitis — meningeal inflammation spreading to optic nerve sheath
• Orbital tumour — compressive, mimics optic neuritis

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5. Post-Infectious / Post-Vaccination

• Childhood vaccinations (measles, mumps, varicella)
• Post-viral syndrome (ADEM spectrum)
• Often bilateral in children; viral infection ~2–4 weeks prior

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6. Special Situations

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Key Differentials of Optic Neuritis

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MS Risk After First Optic Neuritis (Optic Neuritis Treatment Trial)

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• Bradley and Daroff's Neurology in Clinical Practice — Typical/atypical optic neuritis; MS; NMOSD; MS risk; OCT
• The Wills Eye Manual — Etiology; differential diagnosis; Uhthoff; signs; MOGAD
• Kanski's Clinical Ophthalmology, 10th Ed. — Demyelinating optic neuritis; NMOSD; MOGAD; Schilder's
• Harrison's Principles of Internal Medicine, 22nd Ed. — NMOSD optic neuritis; visual loss
• Tintinalli's Emergency Medicine — Infectious causes; post-vaccination; workup
• Goldman-Cecil Medicine — Systemic inflammatory and infectious associations

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30. DM - Neurology — Combined Rank List

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• "—" means that roll number did not appear in the visible portion of the other list (may be on a page not shown).
• The images show only partial data — image 1 shows AML Ranks 1–27, image 2 shows CML Ranks 1–26. Some roll numbers appear in one list but not the other within the visible range.
• AML Rank = based on Total Marks out of 100 (includes practical/viva).
• CML Rank = based on Theory Marks out of 80 only.