Peripheral Neuropathy

Populations and Risk Factors

• Diabetes mellitus — the single most common cause; diabetic peripheral neuropathy affects approximately 50% of people with long-standing diabetes; risk increases with poor glycemic control, duration of disease, and presence of other microvascular complications
• Chronic alcoholism — direct neurotoxic effect of ethanol plus associated nutritional deficiency (thiamine/B1, B12); second most common cause in developed countries
• Vitamin B12 deficiency — from pernicious anemia, vegan diet, gastric bypass surgery, or metformin use; produces combined peripheral neuropathy and posterior column (spinal cord) degeneration
• Chronic kidney disease — uremic neuropathy; toxin accumulation damages peripheral nerves
• Chemotherapy-induced — vincristine, cisplatin, taxanes, and other agents are directly neurotoxic; dose-limiting side effect of many cancer treatments
• Heavy metal exposure — lead, mercury, arsenic, thallium
• Infections — herpes zoster (postherpetic neuralgia), HIV/AIDS, Lyme disease, leprosy
• Autoimmune — GBS (acute), chronic inflammatory demyelinating polyneuropathy (CIDP, chronic)
• Hereditary — Charcot-Marie-Tooth disease (most common hereditary neuropathy)
• Idiopathic — approximately 20–30% of cases have no identifiable cause despite thorough workup
• Age — prevalence increases significantly over age 55

Causes and Pathophysiology

Demyelinating vs. Axonal Neuropathy

• Demyelinating neuropathy: Schwann cells or their myelin sheaths are the primary target. Segmental demyelination slows or blocks nerve conduction velocity (NCV) — measurable on nerve conduction studies. Because the axon itself is initially preserved, remyelination can restore function, and recovery potential is better. Classic example: GBS (acute) and CIDP (chronic).
• Axonal neuropathy: The axon itself degenerates, either from the cell body outward (neuronopathy) or from the terminal backward (dying-back neuropathy). Axonal degeneration is slower to recover because regeneration requires axonal regrowth (~1 mm/day from the site of injury). Classic example: diabetic neuropathy, toxic neuropathy, alcoholic neuropathy.
• Mixed: Many neuropathies involve both demyelination and axonal damage, particularly as the disease progresses.
• Nerve conduction velocity (NCV): The diagnostic test that differentiates demyelinating (slowed conduction, prolonged latencies) from axonal (reduced amplitude with preserved conduction velocity) neuropathy. MTs do not perform NCV studies but should understand the distinction because it determines prognosis.

Length-Dependent ("Dying-Back") Neuropathy

• In systemic conditions (diabetes, alcohol, toxins), the longest axons are most vulnerable because they have the greatest metabolic demand, the longest transport distances for nutrients and waste, and the most exposure to circulating toxins. The sensory neurons supplying the feet have the longest axons in the body — therefore the feet are affected first.
• As the disease progresses, the "dying-back" front advances proximally — from feet to lower legs, then from fingertips to hands, producing the characteristic glove-and-stocking distribution. By the time hand symptoms appear, lower leg involvement is typically well established.
• This length-dependent pattern is a key diagnostic feature: if hand symptoms appear before foot symptoms, the neuropathy is not length-dependent and a different mechanism should be suspected (entrapment, multifocal, or neuronopathy).

Fiber-Type Progression: Sensory → Motor → Autonomic

• Small sensory fibers (unmyelinated C-fibers and thinly myelinated A-delta fibers) are typically affected first — they carry pain, temperature, and crude touch. Early symptoms are burning pain, temperature hypersensitivity, and paresthesia.
• Large sensory fibers (myelinated A-beta fibers) follow — they carry proprioception, vibration sense, and fine touch. Loss of proprioception and vibration sense produces balance difficulties, stumbling, and positive Romberg's test. Loss of protective sensation leads to unrecognized tissue injury (foot ulcers in diabetic neuropathy).
• Motor fibers are affected later — producing weakness, muscle wasting (visible in intrinsic foot muscles first), and hyporeflexia. Foot drop may develop from peroneal nerve motor fiber loss.
• Autonomic fibers are the last to be clinically recognized but may be affected early in diabetic neuropathy specifically — producing anhidrosis (dry skin, cracking), vasomotor instability (cold feet, dependent rubor), gastroparesis, orthostatic hypotension, cardiac arrhythmias, and bladder/bowel dysfunction. Autonomic neuropathy is the most dangerous subtype because of its cardiovascular consequences.

The Pain Paradox

• Peripheral neuropathy produces the counterintuitive combination of numbness AND pain in the same distribution. This occurs because different fiber types are affected at different rates: small pain-carrying fibers may become hyperexcitable (ectopic firing, central sensitization) while large sensory fibers are losing protective sensation.
• Neuropathic pain mechanisms: damaged nerves generate spontaneous ectopic discharges (burning, shooting pain without stimulus); loss of large fiber inhibition removes the normal "gate control" modulation of pain signals; central sensitization develops as the spinal cord dorsal horn becomes hyperexcitable from chronic nociceptive input.
• Clinically, this means: the patient has areas that are both numb to light touch AND burning or hypersensitive to pressure — the therapist cannot rely on absence of pain response to mean absence of tissue damage.

Mononeuropathy vs. Polyneuropathy

• Mononeuropathy: Single nerve affected — usually from compression (carpal tunnel, cubital tunnel) or trauma. Distribution matches the specific nerve territory. Not length-dependent.
• Polyneuropathy: Multiple nerves affected symmetrically — the pattern described above (glove-and-stocking). Usually systemic cause.
• Mononeuropathy multiplex: Multiple individual nerves affected in a patchy, asymmetric pattern — suggests vasculitis, diabetes, or sarcoidosis; requires urgent medical evaluation.
• Double crush phenomenon: Compression at one site along a nerve (e.g., cervical root) makes the nerve more vulnerable to compression at a second site (e.g., carpal tunnel) due to impaired axoplasmic flow. A patient may have both cervical radiculopathy and carpal tunnel syndrome simultaneously, each worsening the other.

Signs and Symptoms

By Fiber Type

Characteristic Clinical Findings

• Glove-and-stocking distribution: Symmetric distal sensory changes beginning in the feet (stocking) and later appearing in the hands (gloves); the defining pattern of length-dependent polyneuropathy
• Trophic changes: Shiny, thin, hairless skin; brittle nails; poor wound healing — resulting from combined sensory denervation, autonomic dysfunction, and microvascular disease
• Foot ulcers: Painless pressure sores on weight-bearing surfaces — the patient cannot feel the tissue damage; this is the most dangerous consequence of sensory loss in diabetic PN and the leading cause of non-traumatic lower limb amputation
• Balance impairment: Loss of proprioceptive input from the feet produces unsteadiness, stumbling, and falls — particularly dangerous in darkness or on uneven surfaces when visual compensation is reduced
• Neuropathic pain: Burning, stabbing, electric, or "pins and needles" sensations; often worse at night; may coexist with numbness (the pain paradox)

Assessment Profile

Subjective Presentation

• Chief complaint: "My feet burn and tingle"; "I feel like I'm walking on cotton"; "My feet are numb but they still hurt" (the pain paradox); "I keep stumbling"; "I can't feel the pedals when I drive"; history typically reveals long-standing diabetes, alcohol use, or other systemic cause
• Pain quality: Burning, electric, stabbing, or "pins and needles" (neuropathic descriptors); worse at night; not relieved by position change; coexists with numbness in the same area; may describe sensitivity to bed sheets touching the feet (allodynia)
• Onset: Gradual, insidious onset over months to years; feet affected first (length-dependent); hands later; progressive unless the underlying cause is treated; the patient may not notice sensory loss until injury occurs
• Aggravating factors: Prolonged standing or walking; night (pain often worsens); heat (may increase burning in some patients); tight footwear; poor glycemic control (diabetic PN worsens with hyperglycemia)
• Easing factors: Elevation may reduce dependent edema; gabapentinoid medications (gabapentin, pregabalin) reduce neuropathic pain but cause sedation and orthostatic hypotension; cool surfaces may reduce burning; movement may reduce cramping
• Red flags: Rapid onset of bilateral weakness → possible GBS; emergency referral. Mononeuropathy multiplex pattern (asymmetric, patchy) → vasculitis workup needed; urgent referral. New foot ulcer or wound the patient was unaware of → wound care referral; do not massage the affected area. Autonomic symptoms (syncope, severe orthostatic hypotension, cardiac palpitations) → medical evaluation for autonomic neuropathy.

Observation

• Local inspection: Trophic skin changes — shiny, thin, hairless skin on the feet and lower legs; brittle or thickened nails; dry cracked skin from anhidrosis; dependent rubor (redness when dependent, pallor when elevated — vasomotor dysfunction); visible muscle wasting of intrinsic foot muscles (hollow between metatarsal heads); foot ulcers on weight-bearing surfaces; calluses over pressure points
• Posture: Wide-based stance to compensate for balance impairment; may grip surfaces with toes (flexor substitution for lost proprioception); cautious, deliberate movement pattern to compensate for sensory uncertainty
• Gait: Wide-based, unsteady gait; high steppage gait if motor involvement produces foot drop; slapping foot contact (loss of proprioceptive feedback — the patient cannot feel ground contact and lifts feet higher to ensure clearance); Romberg-positive pattern — gait worsens markedly with eyes closed or in darkness

Palpation

• Tone: Hypotonic in affected muscles — LMN pattern; reduced resting tone in intrinsic foot muscles and distal lower leg muscles; no spasticity (distinguishes from MS, stroke); compensatory hypertonia in proximal muscles that overwork to stabilize the trunk and limbs; calf muscles may cramp from motor fiber irritability
• Tenderness: The pain paradox creates a dual palpation challenge. Areas of neuropathic hypersensitivity may be acutely tender to light touch that would be comfortable for a neurologically intact patient. Adjacent numb areas produce no tenderness response despite potentially harmful pressure levels. Always perform a sensory screen before applying therapeutic pressure. Compensatory muscles (proximal lower extremity, lumbar extensors, hip stabilizers) are tender from altered gait mechanics.
• Temperature: Cool extremities — especially feet — from autonomic vasomotor dysfunction and reduced activity; the temperature gradient (warm proximal, cool distal) parallels the neuropathy distribution; poor capillary refill in severe cases; do not rely on the client's temperature perception (they may not feel cold accurately)
• Tissue quality: Trophic changes palpable — thin, atrophic skin with reduced subcutaneous tissue padding over bony prominences. Edema common in dependent distal extremities from autonomic dysfunction. Intrinsic foot muscle atrophy creates palpable hollowing between metatarsal heads. Fascial restrictions develop in chronically shortened muscles.

Motion Assessment

• AROM: Distal weakness produces reduced active range — ankle dorsiflexion weakness (foot drop), toe extension weakness, grip strength decline; proximal range is typically preserved until advanced disease; balance impairment is evident during single-leg stance or tandem walking; proprioceptive loss produces dysmetria (overshooting targets) in finger-nose tests
• PROM / end-feel: Generally normal elastic end-feel unless secondary contractures have developed; PROM exceeds AROM in weakened muscles; ankle joint may show tissue stretch end-feel from chronic plantarflexion posturing; joint hypermobility may develop at MTP joints from intrinsic muscle atrophy (claw toe deformity)
• Resisted testing: LMN-pattern distal weakness — ankle dorsiflexors, evertors, and toe extensors weakest; progressive decline from distal to proximal over time; no pain on resisted testing (unless secondary MSK strain); reflexes diminished (hyporeflexia) or absent (areflexia) — DTR testing is a critical component

Special Test Cluster

Sensory screening before treatment: Before applying any therapeutic pressure to an area with reported sensory changes, perform a simple screening: light touch in the area and ask the patient to describe what they feel. If they cannot feel light touch, they cannot provide reliable feedback about deeper pressure — treat that area with extreme caution using only conservative pressure.

Differential Assessment