Peripheral Neuropathy

Dysfunction of peripheral nerves: classified by distribution (mononeuropathy - single nerve; mononeuritis multiplex - multiple individual nerves, asymmetric; polyneuropathy ; symmetric, length-dependent, most common pattern) and fiber type affected (sensory, motor, autonomic, or mixed).

Common causes: diabetes (most common cause overall, length-dependent sensorimotor pattern), alcohol excess, vitamin deficiency (B12, thiamine, B6 ; either deficiency or excess causing toxicity), chronic kidney disease, hypothyroidism, medications (chemotherapy m-platinum agents/vincristine/taxanes, isoniazid, amiodarone), autoimmune (Guillain-Barré ; acute, CIDP; chronic), hereditary (Charcot-Marie-Tooth), infectious (HIV, leprosy), paraneoplastic, idiopathic (significant proportion despite workup).

• Sensory: numbness, tingling/paresthesia, burning pain, allodynia; classically length-dependent ("glove and stocking" ; feet before hands, distal before proximal)

• Motor: weakness, muscle wasting, reduced/absent reflexes, foot drop in advanced cases

• Autonomic: orthostatic hypotension, gastroparesis, bladder dysfunction, erectile dysfunction, abnormal sweating ; particularly diabetic autonomic neuropathy

• Gait disturbance/falls from proprioceptive loss

• Red flags for urgent workup: rapid progression (days-weeks ; consider Guillain-Barré, urgent neurology), asymmetric/non-length-dependent pattern (consider mononeuritis multiplex; vasculitis workup), significant motor weakness out of proportion to sensory symptoms, autonomic instability with rapid progression

• History: onset pattern/tempo, distribution, medication/alcohol/toxin exposure, family history, systemic symptoms

• Examination: sensory modalities (light touch, pinprick, vibration, proprioception), reflexes, motor strength, gait

• First-line bloods: FBC, glucose/HbA1c, B12 (± methylmalonic acid if borderline), renal function, TSH, LFTs (alcohol marker)

• Further workup if initial negative/atypical: serum protein electrophoresis, ANA/ANCA (vasculitis), HIV, folate, copper (if bariatric surgery history)

• Nerve conduction studies/EMG: distinguishes demyelinating vs. axonal pattern, confirms polyneuropathy vs. mimickers, localizes mononeuropathy

• Nerve biopsy: reserved for specific specialist indications (suspected vasculitis, amyloidosis)

Differentials: myelopathy (spinal cord ; upper motor neuron signs, sensory level), myopathy (proximal weakness, normal sensation), multiple sclerosis, B12 deficiency causing subacute combined degeneration (see separate entry).

• Treat underlying cause: optimize glycemic control (diabetes ; slows progression, doesn't reverse established damage), B12 replacement if deficient, alcohol cessation, address renal/thyroid dysfunction, discontinue causative medication if identifiable

• Neuropathic pain management: gabapentin (titrate to 300-3600mg/day divided), pregabalin (150-600mg/day divided), duloxetine 60mg od (particularly good evidence in diabetic neuropathy), amitriptyline 10-75mg nocte ; first-line agents, individualize by comorbidity/side-effect profile

• Topical options for localized pain: capsaicin cream, lidocaine patches

• Avoid long-term opioids for chronic neuropathic pain (poor evidence, dependence risk)

• Physical therapy: gait training, fall prevention, orthotics for foot drop

• Foot care education (diabetic neuropathy): daily inspection, appropriate footwear, podiatry; critical for ulcer/amputation prevention given reduced protective sensation

• Autonomic symptom management: fludrocortisone/midodrine for orthostatic hypotension, prokinetics for gastroparesis

Referral: neurology for diagnostic uncertainty, rapid progression, asymmetric pattern, suspected inflammatory/autoimmune cause requiring specific treatment (IVIG for GBS/CIDP); podiatry for diabetic foot care.