⚡ Motor Neuropathies — Complete High-Yield Overview
Motor neuropathies cause pure or predominant motor weakness due to disorders of motor axons, occasionally mimicking motor neuron disease.
🔷 1. Immune-Mediated Motor Neuropathies
- AMAN – Acute Motor Axonal Neuropathy (GBS variant)
- AMSAN – Motor-predominant axonal variant
- MMN – Multifocal Motor Neuropathy (🧪 anti-GM1)
- MADSAM – Motor-dominant Lewis–Sumner variant
- CIDP – Motor-predominant chronic inflammatory demyelinating polyneuropathy
Autoimmune Nodopathies (Node/Paranode Antibodies)
- Anti-NF155
- Anti-CNTN1
- Anti-Caspr1
Other immune causes
- Vasculitic motor neuropathy
- Paraneoplastic motor neuropathy:
- Anti-Hu
- Anti-CRMP5
🧬 2. Hereditary Motor Neuropathies
- dHMN – Distal hereditary motor neuropathies
- CMT Type 2 (axonal; often motor-heavy)
- CMT X – Some variants predominantly motor
- SMA-like hereditary motor neuropathies
- Kennedy disease (SBMA) – Motor neuropathy + androgen receptor defect
☣️ 3. Metabolic / Toxic Motor Neuropathies
- Porphyric neuropathy – Acute motor > sensory
- Heavy metals: arsenic, thallium
- Lead neuropathy – Classically causes wrist/foot drop
- Organophosphate poisoning
- Drug-induced motor neuropathy:
- Vincristine
- Paclitaxel
- Amiodarone (rare)
- Dapsone (rare motor)
- Thyrotoxic neuropathy
- Vitamin B6 toxicity (sensory ± motor)
🦠 4. Infectious Motor Neuropathies
- Diphtheritic neuropathy (toxin-mediated; predominantly motor)
- Poliovirus / polio-like enteroviruses
- West Nile virus motor neuropathy
- HIV motor axonal neuropathy
- CMV motor polyradiculopathy (immunocompromised)
- Zika-associated motor GBS
⚙️ 5. Motor Neuropathies Mimicking NMJ or MND
(Pure motor presentation may resemble neuropathy)
- ALS with peripheral motor features
- Adult SMA (Type IV)
- PLS variants (rare LMN involvement)
🦵 6. Structural / Compressive Motor Neuropathies
- Entrapment neuropathies (motor-predominant):
- Ulnar neuropathy at elbow
- Radial palsy (Saturday night palsy)
- Common peroneal palsy
- Traumatic nerve injury
- Iatrogenic injury (surgery, nerve blocks)
🌐 7. Systemic / Miscellaneous Motor Neuropathies
- Diabetic pure motor neuropathy (rare)
- Thyroid storm–associated neuropathy
- Critical illness polyneuropathy (motor-predominant forms)
- Sarcoid motor neuropathy
- Amyloidosis (motor-heavy variants)
- Channelopathies affecting motor axonal conduction
🧠 Easy Mnemonic: “HIT MIMICS” — Causes of Motor Neuropathy
H – Hereditary (dHMN, CMT)
I – Immune (MMN, CIDP, AMAN)
T – Toxic (lead, porphyria, chemotherapy)
M – Metabolic (thyrotoxicosis, B6 toxicity)
I – Infectious (diphtheria, polio, West Nile)
M – Malignant / Paraneoplastic
C – Compressive neuropathies
S – Systemic (diabetes, sarcoidosis, amyloid)
