What is the diagnostic workup for a patient presenting with bilateral numbness of toes and fingers?

Diagnostic Workup for Bilateral Numbness of Toes and Fingers

The diagnostic workup for bilateral numbness of toes and fingers should begin with laboratory testing including blood glucose, serum B12 with methylmalonic acid and homocysteine, complete blood count, comprehensive metabolic panel, thyroid function tests, and serum protein immunofixation electrophoresis, as these tests have the highest diagnostic yield for identifying the underlying cause. 1

Initial Clinical Assessment

When evaluating a patient with bilateral numbness in the toes and fingers, focus on:

• Distribution pattern: Confirm if it follows a "stocking-and-glove" distribution, which is characteristic of peripheral neuropathy 2
• Associated symptoms: Assess for:
  • Pain or burning sensations
  • Weakness
  • Autonomic symptoms (orthostatic hypotension, bladder/bowel dysfunction)
  • Gait disturbances
• Risk factors: Identify:
  • Diabetes mellitus (most common cause of distal symmetric polyneuropathy) 3
  • Alcohol consumption
  • Medication history (especially chemotherapeutic agents)
  • Vitamin deficiencies
  • Exposure to toxins

Laboratory Evaluation

The following laboratory tests should be ordered:

1. Blood glucose and HbA1c (highest yield at 11% abnormal results) 1
2. Serum B12 with methylmalonic acid and homocysteine (even with normal B12 levels between 200-500 pg/dL) 1
3. Complete blood count
4. Comprehensive metabolic panel
5. Thyroid function tests
6. Serum protein immunofixation electrophoresis (abnormal in approximately 9% of patients with distal symmetric polyneuropathy) 1
7. Erythrocyte sedimentation rate

Neurological Examination

Perform a thorough neurological examination focusing on:

1. Sensory testing:

   • 10-g monofilament test
   • Vibration testing using a 128-Hz tuning fork
   • Pinprick sensation
   • Temperature sensation 4

2. Motor testing:

   • Muscle strength assessment
   • Deep tendon reflexes (often reduced or absent in peripheral neuropathy) 4

3. Coordination and gait assessment

Specialized Testing

Based on initial findings, consider:

1. Electrodiagnostic studies (EMG/NCS):

   • To differentiate between axonal and demyelinating neuropathies
   • To assess severity and distribution of nerve involvement 1

2. Vascular assessment:

   • Ankle-brachial index (ABI) if signs of vascular insufficiency are present
   • Particularly important for patients over 50 years or under 50 with PAD risk factors 1

3. Advanced imaging:

   • MRI of the spine if radiculopathy is suspected
   • Brain MRI if central causes are suspected 4

Disease-Specific Considerations

For diabetic neuropathy suspicion:

• Comprehensive foot examination including skin inspection for ulcers or calluses
• Assessment of foot deformities
• Evaluation for loss of protective sensation 4

For chemotherapy-induced neuropathy:

• Detailed medication history focusing on neurotoxic agents (especially paclitaxel and oxaliplatin)
• Assessment of symptom progression pattern (worsening during treatment vs. after completion) 4

For autonomic neuropathy:

• Orthostatic blood pressure measurements
• Heart rate variability testing if cardiovascular autonomic neuropathy is suspected 5

Common Pitfalls to Avoid

1. Failing to differentiate peripheral from central causes: Bilateral numbness can sometimes be caused by central nervous system disorders rather than peripheral neuropathy.

2. Missing non-length-dependent neuropathies: Not all neuropathies follow the classic stocking-and-glove distribution; some may present with proximal symptoms or patchy distribution.

3. Overlooking treatable causes: Vitamin B12 deficiency, hypothyroidism, and diabetes are treatable causes that should not be missed.

4. Incomplete autonomic testing: Autonomic symptoms often accompany sensory neuropathies but may be overlooked if not specifically assessed.

By following this systematic approach, you can efficiently identify the underlying cause of bilateral numbness in the toes and fingers, leading to appropriate treatment and management strategies.