What is the workup for a patient with numbness in the lower (L) foot at night?

Workup for Nighttime Foot Numbness

Initial Assessment

The workup for a patient with numbness in the lower foot at night should begin with a thorough neurological examination, including 10-g monofilament testing or Ipswich touch test with at least one additional assessment (pinprick, temperature, or vibration using a 128-Hz tuning fork), and vascular assessment including pulses in the legs and feet. 1

History Taking

• Ask about the pattern of numbness: onset, duration, progression, and whether it's relieved by movement 1
• Assess for other associated symptoms such as pain, burning, weakness, or skin changes 1
• Inquire about specific nighttime symptoms that may suggest restless legs syndrome (RLS):
  • Whether the discomfort is relieved by movement 1
  • Whether symptoms return after sitting or lying down 1
  • Whether symptoms are worse in the evening or night 1
• Obtain history of diabetes, smoking, alcohol use, medications, and family history of neuropathy 1, 2

Physical Examination

Neurological Assessment

• Perform 10-g monofilament testing at multiple sites on the foot (a simplified 8-site test detects 90% of abnormalities compared to the full 16-site test) 3
• Test vibration sensation using a 128-Hz tuning fork 1
• Assess pinprick and temperature sensation 1
• Test deep tendon reflexes, especially ankle reflexes 2

Vascular Assessment

• Palpate peripheral pulses (femoral, popliteal, dorsalis pedis, and posterior tibial) 1, 2
• Assess for capillary refill time, rubor on dependency, pallor on elevation, and venous filling time 1
• Look for signs of peripheral arterial disease (PAD) such as decreased walking speed, leg fatigue, or claudication 1

Skin and Foot Inspection

• Inspect for skin integrity, color changes, calluses, or wounds 1
• Assess for foot deformities that may contribute to symptoms 1
• Look for signs of infection or ulceration 1

Diagnostic Testing

First-Line Testing

• Ankle-brachial index (ABI) if vascular disease is suspected 1
• Blood tests: electrolytes, renal function, thyroid function, HbA1c, calcium, and ferritin levels 1
  • Ferritin values less than 50 ng/mL are consistent with RLS and suggest the need for iron supplementation 1
• Urine dipstick for proteinuria and hematuria 1

Additional Testing Based on Initial Findings

• If PAD is suspected: toe pressures, skin perfusion pressure, or transcutaneous oxygen pressure (TcPO2) 1
• If diabetic neuropathy is suspected: comprehensive foot examination 1
• If RLS is suspected and initial tests are negative: consider sleep study to rule out periodic limb movements during sleep 1
• If neurological symptoms are prominent: consider nerve conduction studies 1

Differential Diagnosis

Common Causes of Nighttime Foot Numbness

• Peripheral neuropathy (especially diabetic) 1
• Restless legs syndrome 1
• Peripheral arterial disease 1
• Nerve compression syndromes (e.g., tarsal tunnel syndrome) 4
• Positional compression during sleep 2

Less Common Causes

• Spinal stenosis or radiculopathy 1
• Vitamin deficiencies (B12, folate) 1
• Autonomic neuropathy 5
• Systemic conditions (e.g., multiple sclerosis, transverse myelitis) 6

Management Approach

The management approach should be directed by the underlying cause:

• For diabetic neuropathy: optimize glycemic control and consider symptomatic treatments like anticonvulsants (pregabalin, gabapentin) or antidepressants (duloxetine) 1
• For RLS: consider dopaminergic agents (ropinirole, pramipexole) if symptoms are severe and impact quality of life 1
• For PAD: address cardiovascular risk factors and consider referral to vascular specialist if symptoms are severe 1
• For positional compression: advise on sleep positioning and proper footwear 2

Follow-up Recommendations

• Patients with evidence of sensory loss or prior ulceration should have their feet inspected at every visit 1
• Those with PAD or neuropathy should be referred to foot care specialists for ongoing preventive care 1
• Provide education on foot self-care and proper footwear 1
• Consider multidisciplinary care for complex cases, especially those with diabetes and multiple risk factors 1

Clinical Pearls

• The 10-g monofilament test is the most useful test to diagnose loss of protective sensation 1
• Nighttime symptoms that improve with movement are characteristic of RLS rather than neuropathy 1
• Absence of the dorsalis pedis pulse can be a normal variant and is less accurate for diagnosis of PAD than absence of the posterior tibial pulse 1
• Comprehensive foot examinations should be performed at least annually for patients with diabetes 1