Acute reversible neuropathy – associated with hyperglycemia and rapid correction of hyperglycemia. Ex: DKA. Improvement is ~50% chance, and can take up to a year to resolve.
Pathophysiology: involves deposition of sorbitol?
Chronic persistent neuropathy:
- Systemic polyneuropathy: classic stocking-glove neuropathy; reduced or lost sensation on monofilament testing; burning or tingling.
- Autonomic neuropathy: smooth muscle; gastroparesis, postural hypotension, bladder dysfunction (urinary incontinence or retention), erectile dysfunction.
DDx of peripheral neuropathy:
- Radiculopathy, spinal stenosis, vitamin B12 deficiency, toxins (EtOH, chemo), hypothyroidism, CRF, multiple myeloma (SPEP, UPEP), malignancies (bronchogenic carcinoma), HIV, CIDP…
Medications Used in Management:
- Pregabalin: presynaptically inhibits excitatory glutamate, substance P.
- Duloxetine: SSNRI – RCTs showed 59% vs 25% placebo; slightly more effective than pregabalin; take at QHS.
- Amitriptyline: dose =/= improvement; titrate patient-specific; average 105mg/day; alters central processing of pain; ~55% reduction in pain vs placebo; anticholinergic side-effects and QT prolongation.
- Nortriptyline: slightly less anticholinergic than amitriptyline; combine with gabapentin – works better than both alone.
- Venlafaxine – likely not helpful.
- Gabapentin – 300 – 900mg TID; doses > 1200mg/d more effective than smaller doses; some studies say it works better than placebo, some doesn’t. Wide therapeutic window.
- Valproic acid: not in pregnancy; no RCTs to support.
- Capsaicin: locally depletes substance P.
- Alpha-lipoic acid: anti-oxidant; RCTs show some benefit; ?reduces oxidative stress on nerve.
- Lidocaine: up to 4 x 5% patches for up to 18 hours.
- TENS units: daily tx x 30 minutes; desensitize nerves through stimulation; trials shows up to modest pain improvement after 6-12 weeks of treatment
- Isosorbide dinitrite spray: topical spray, improves peripheral circulation
- Acetyl-L-carnitine: ?inhibits signals that causes senescence in cells; take with ALA – to counteract free radical formation, no data to support.