PERIPHERAL NEUROPATHIES


See also "Carpal Tunnel Syndrome," "Diabetic Neuropathy," and "Trigeminal Neuralgia"

I. Pathophysiology

  1. Some loss of sens. (esp. vibr--large fibers) & reflex fn with age; more in distal reaches
    1. Complaints are rare in age-related periph. neuropathy, so complaints us. represent diff. disease process
  2. Autonomic periph. neuropathy presents with gastric sx; impotence, urinary retention, change in sweating, & pupillary abnormalities
  3. Axonal vs. demyelinating neuropathies (axonal more common; demyelinating, e.g. Guillain-Barre, more amenable to fnal recovery)
    1. Distinguish between by EMGs
    2. W/U for axonal neuropathies: CBC, SMA20, VDRL, tests for collagen-vascular diseases, TFTs, B12, maybe LP & nerve bx

II. Causes of axonal neuropathies:

  1. Diabetes Mellitus (click link for more information on diabetic neuropathy)
  2. Hypothyroidism-can present with Carpal Tunnel Syndrome!
  3. Renal failure
  4. Paraproteinemias, e.g. from Multiple Myeloma
  5. Nutritional deficiency, e.g. B12, B6 (risk factors include alcoholism and isoniazid use)
  6. Vasculitides-e.g. from Lupus, Lewy's disease, infectious (e.g. herpes zoster)
  7. Toxins-lead and other heavy metals, cisplatin, N2O
  8. Hereditary neuropathies
  9. Cancer--incidence of cancer in a series of 51 pts (mean age 65) with unexplained sensory neuropathy (proven with nn-conduction studies) was 35%: hepatoma, lymphoma, and bladder ca's were most common (Arch. Neurol. 55:981, 1998--JW)

III. Treatments

  1. Tricyclic antidepressants
  2. Gabapentin
  3. Analgesics including opiate analgesics
  4. Cannabinoids
    1. In a randomized trial of CT-3, 1 wk counrses of a synthetic THC analogue, vs. placebo, in 21 adults with chronic neuropathic pain, CT-3 was ass'd with sig. greater reductions in pain scores (JAMA 290:1757, 2003--AFP)

Note-Skin biopsy with special stains to determine epidermal nerve fiber density, may be a useful way to identify "small fiber" neuropathies that might not appear on nerve-conduction studies (Neurol. 53:1641, 1999--JW) or sural nerve biopsy (Neurol. 53:1634, 1999--JW)