Peripheral Neuropathy: Nerve Damage Outside the Central Nervous System

Peripheral neuropathy is damage to the peripheral nerves — the vast network outside the brain and spinal cord (central nervous system) that connects the CNS to the rest of the body.

Anatomical Distribution

• Sensory nerves: Carry touch, pain, temperature, proprioception from skin, joints, muscles to CNS.
• Motor nerves: Carry signals from CNS to skeletal muscles for voluntary movement.
• Autonomic nerves: Control involuntary functions (HR, BP, digestion, sweating, bladder).

Neuropathy can affect one type (pure sensory, pure motor, autonomic) or multiple (sensorimotor, mixed).

Common Patterns

• Length-dependent (stocking-glove): Distal symmetric polyneuropathy — starts in toes/feet, ascends; then hands. Most common (diabetes, idiopathic).
• Mononeuropathy: Single nerve (carpal tunnel, ulnar at elbow, peroneal at fibular head).
• Mononeuritis multiplex: Multiple individual nerves sequentially (vasculitis, diabetes, sarcoid).
• Plexopathy: Brachial/lumbosacral plexus (trauma, compression, radiation, tumor).
• Radiculopathy: Nerve root (disc herniation, stenosis) — technically root, not peripheral nerve, but often grouped.

Major Etiologies

• Diabetes mellitus (most common cause)
• Alcohol use disorder
• Nutritional deficiencies (B12, B1, B6, E, copper)
• Autoimmune (Guillain-Barré, CIDP, vasculitis)
• Infections (HIV, Lyme, leprosy, shingles)
• Toxins (chemotherapy — platinum, taxanes; heavy metals)
• Hereditary (Charcot-Marie-Tooth)
• Compressive/entrapment
• Idiopathic

Diagnosis

• History, neurological exam (sensory, motor, reflexes).
• Nerve conduction studies (NCS) + electromyography (EMG) — gold standard.
• Labs: Glucose, HbA1c, B12, TSH, ESR, SPEP, vitamin levels.
• Skin biopsy (intraepidermal nerve fiber density) for small fiber neuropathy.

Management

Treat underlying cause; symptomatic pain control (gabapentinoids, SNRIs, TCAs, topical lidocaine/capsaicin); physical therapy; foot care (diabetes); assistive devices.