What is the typical diagnosis of peripheral neuropathy of the foot?

Diagnosis of Peripheral Neuropathy of the Foot

The diagnosis of peripheral neuropathy of the foot is established clinically using the 10-g monofilament test combined with at least one additional bedside neurological assessment (pinprick, temperature, vibration with 128-Hz tuning fork, or ankle reflexes), with absent monofilament sensation plus one other abnormal test confirming loss of protective sensation (LOPS). 1

Clinical Diagnostic Approach

Essential History Elements

Document the following specific factors that increase neuropathy risk 1:

• Diabetes control and duration (screen at diagnosis for type 2 diabetes, 5 years after diagnosis for type 1 diabetes) 1
• Smoking history
• Prior foot ulcerations or amputations
• Symptoms of neuropathy: pain, burning sensations, numbness, dysesthesias 1
• Exercise tolerance and claudication (to assess for concurrent peripheral arterial disease)
• Medication exposures (neurotoxic drugs), alcohol use, vitamin B12 deficiency 1

Physical Examination Components

The comprehensive foot examination must include four key assessments 1:

1. Skin integrity assessment: Look for ulcerations, calluses, deformities (bunions, hammertoes, prominent metatarsals) 1

2. Neurological testing for LOPS (the single most common cause of foot ulceration in 78% of diabetic foot ulcers) 1:

   • 10-g monofilament test (most sensitive bedside test) applied to the dorsal aspect of the hallux, moving proximally until threshold detected 1
   • Plus at least one of: pinprick sensation, temperature perception, vibration with 128-Hz tuning fork, or ankle reflexes 1
   • Diagnostic criterion: Absent monofilament sensation AND one other abnormal test confirms LOPS 1

3. Vascular assessment: Palpation of dorsalis pedis and posterior tibial pulses, capillary refill time, rubor on dependency, pallor on elevation, venous filling time 1

4. Foot deformity assessment: Identify structural abnormalities that increase plantar pressures 1

When Advanced Testing Is NOT Needed

A critical caveat: Further neurological testing (nerve conduction studies, electromyography, nerve biopsy, or intraepidermal nerve fiber density biopsies) is rarely indicated for diagnosing peripheral sensory neuropathy in the foot. 1 These specialized tests are reserved only for atypical presentations or when the diagnosis remains unclear after clinical assessment 1.

Screening Frequency Based on Risk Stratification

The International Working Group on the Diabetic Foot provides clear examination intervals 1:

• Category 0 (no LOPS, no PAD): Annually
• Category 1 (LOPS or PAD): Every 6-12 months
• Category 2 (LOPS + PAD, or LOPS + foot deformity, or PAD + foot deformity): Every 3-6 months
• Category 3 (LOPS or PAD plus history of ulcer, amputation, or end-stage renal disease): Every 1-3 months

Differential Diagnosis Considerations

In patients with severe or atypical neuropathy patterns, alternative etiologies must be excluded 1:

• Neurotoxic medications
• Heavy metal poisoning
• Chronic alcohol abuse
• Vitamin B12 deficiency
• Renal disease
• Chronic inflammatory demyelinating neuropathy
• Inherited neuropathies
• Vasculitis

Key Clinical Pitfall

The most common error is failing to perform the monofilament test with a second confirmatory neurological assessment. A single abnormal test is insufficient—you need both absent monofilament sensation AND at least one other abnormal neurological finding to confirm LOPS. 1 This two-test requirement prevents overdiagnosis while maintaining high sensitivity (>87%) for detecting clinically significant neuropathy 1.