Toxic or Drug Induced Neuropathy

Toxic/Drug Induced Neuropathy

Many drugs, toxins and environmental chemicals can produce a peripheral neuropathy, with or without other manifestations.

Industrial/environmental agents:
Arsenic:
• chronic exposure  malaise, burning sensation and sensory loss in ‘stocking and glove’ distribution; garlic odour of breath (if high dose); loss of plantar foot reflexes; hyperkeratosis of hands and feet; also get a vasculitis  “black foot disease”; white transverse striations of nails (Mees lines)
• more common in industries which arsenic is involved (eg copper smelting)
• can mimic Guillain-Barre syndrome
• treatment – chelation

Acrylamide:
• skin exposure is neurotoxic (impairs axoplasmic transport); often have a dermatitis of hands
• numbness (loss of vibration sense is most noticeable; stocking & glove distribution), weakness, gait ataxia, hyperhidrosis of feet and hands, diffuse areflexia
• withdrawal from exposure  slow recovery (some weakness or sensory loss may remain)

Lead:
• lead binds to sulfur groups  disruption of enzymes; produces demyelination
• chronic exposure  anaemia, colic, neuropathy
• neuropathy is mostly motor – affects mostly arm, but foot plantarflexors and peroneals may affected; starts with bilateral weakness; may have symmetrical sensory loss (could be subclinical, affecting legs>arms)

Mercury:
• if inhaled  toxic; used in electrical and chemical industries
• get a peripheral motor dysfunction and painful dysthaesias – especially distally; tremor
• mimics Guillain-Barre syndrome

Methyl bromide:
chronic exposure to high to moderate levels  distal sensory and motor neuropathy (symmetric numbness, parathesias, distal weakness, calf muscle tenderness)
also have pyramidal tract signs and signs of cerebellar dysfunction
resolves following withdrawal from exposure

Others:
• carbon disulfide (usually a lower limb numbness, parathesia and weakness); cadmium (often a subclinical motor and sensory neuropathy); dimethylaminopropionitrile; ethylene oxide (stocking and glove parathesia; mild motor changes); hexacarbons (distal weakness; parathesias in hands and feet; ankle reflexes lost); vacor (rapid onset of weakness with mild sensory loss); cyanide (neuropathy presents with dysthesias in feet; insidious onset; ataxia some weakness and muscle wasting; reduced reflexes); allyl chloride (distal neuropathy; sensory>motor; recovery after withdrawal of agent); thallium (reflexes generally normal; pain and parathesias in legs; weakness is mild)

Glue Sniffer Syndrome:
Exposure to n-Hexane occurs due to inhalation; muscle weakness – can progress o quadriplegia in severe cases; autonomic involvement of hands and feet – hyperhidrosis, blue discoloration, Mee’s lines in nails; feet and hands feel cooler

Drugs:
Colchicine:
• used to treat gout
• inhibits axonal flow by inhibiting microtubule formation
• mild distal sensory peripheral neuropathy and myopathy – usually mild

Chloroquine:
• antimalarial and used in autoimmune diseases
• neuropathy can develop after 1-2 years use
• can get a mild, painless proximal muscle weakness – buy may also get a mild distal mixed sensorimotor polyneuropathy

Gold:
• used for rheumatoid arthritis – side effects are common
• peripheral neuropathy is rare complication – usually a burning sensation, pain or loss of distal sensation

Phenytoin:
• antiepileptic
• most will show mild sensory loss on plantar surface of feet and diminished deep tendon reflexes
• can develop dysesthesias and mild weakness – especially distal legs

Statins:
lipid lowering drugs
neuropathy can develop after several years of use
sensory loss affecting feet greater than the hands; parathesias; distal weakness; occasional gait instability