Neuropathies
Also known as: peripheral neuropathy
Neuropathies are disorders of the peripheral nerves that disrupt sensory, motor, or autonomic signaling. Symptoms range from numbness, tingling, and burning pain to weakness, and diabetes is the most common cause.
A neuropathy is damage or dysfunction of the peripheral nerves — the nerves outside the brain and spinal cord. Depending on which fibers are affected, neuropathies produce sensory symptoms (numbness, tingling, burning pain), motor symptoms (weakness, atrophy), autonomic symptoms (orthostatic hypotension, abnormal sweating, gastrointestinal dysmotility), or a mix.
Neuropathies are classified by distribution. A mononeuropathy affects a single nerve, as in carpal tunnel syndrome's compression of the median nerve. Mononeuritis multiplex affects several individual nerves asymmetrically. A polyneuropathy affects many nerves symmetrically, typically longest fibers first — producing the classic distal "stocking-glove" pattern. Mechanistically, damage may be axonal (degeneration of the nerve fiber itself) or demyelinating (loss of the myelin sheath, as in Guillain-Barré syndrome).
Causes are diverse: diabetes mellitus is the most common, and others include chronic alcohol use, vitamin B12 deficiency, autoimmune disease, hereditary conditions such as Charcot-Marie-Tooth, and medications — notably chemotherapeutic agents like vincristine, cisplatin, and paclitaxel, whose dose-limiting toxicity is often peripheral neuropathy.
USMLE Step 1 tests neuropathy patterns, mechanisms, and drug causes within nervous system pathology and pharmacology. The CCMA touches neuropathy in endocrinology, since diabetic patients need routine foot examination, and the PTCE covers neuropathy as a hallmark adverse effect of antineoplastic drugs.
Key takeaways
- Neuropathies are peripheral nerve disorders producing sensory, motor, or autonomic dysfunction.
- Mononeuropathy affects one nerve; polyneuropathy affects many symmetrically, often in a stocking-glove pattern.
- Damage is either axonal or demyelinating — Guillain-Barré syndrome is the classic acute demyelinating example.
- Diabetes is the most common cause; alcohol, B12 deficiency, hereditary disease, and chemotherapy drugs are other major causes.
- USMLE Step 1, the CCMA, and the PTCE test neuropathies through pathology, diabetic care, and chemotherapy side effects respectively.