What is the diagnosis for a diabetic patient with numbness that started in one foot, spread to one lower extremity, and then one upper extremity?

Diagnosis: Diabetic Mononeuropathy Multiplex

This diabetic patient presenting with asymmetric numbness that began in one foot and sequentially spread to one lower extremity and then one upper extremity most likely has diabetic mononeuropathy multiplex, not the typical distal symmetric polyneuropathy. 1

Key Distinguishing Features

The asymmetric, sequential pattern of nerve involvement is the critical diagnostic clue that differentiates this presentation from typical diabetic peripheral neuropathy:

• Typical diabetic neuropathy presents with symmetric "glove and stocking" distribution affecting both feet simultaneously, then progressing proximally in a length-dependent pattern 2, 3
• Mononeuropathy multiplex presents with asymmetric involvement of individual nerves or nerve territories in a sequential, non-length-dependent pattern 1
• The progression from one foot → one lower extremity → one upper extremity indicates multiple discrete nerve territories are affected rather than a diffuse symmetric process 1

Underlying Pathophysiology

• Mononeuropathy multiplex results from vascular insufficiency causing ischemic infarction of the vasa nervosa (blood vessels supplying individual nerves), rather than the metabolic dysfunction seen in symmetric polyneuropathy 4
• This vascular mechanism explains the acute onset and asymmetric distribution pattern 4

Essential Diagnostic Workup

Perform a focused neurologic examination to confirm the diagnosis and map affected nerve territories 1:

• Test pinprick sensation to assess small fiber function 1
• Test vibration perception using a 128-Hz tuning fork to assess large fiber function 2, 1
• Assess ankle reflexes and reflexes in affected extremities 2, 1
• Document the specific distribution of sensory loss to identify which individual nerves are affected 1

Critical Alternative Diagnoses to Exclude

Before confirming diabetic mononeuropathy multiplex, rule out other causes 1:

• Entrapment neuropathies (carpal tunnel syndrome, ulnar neuropathy, peroneal neuropathy at the fibular head) - these can occur more frequently in diabetic patients 4
• Vitamin B12 deficiency - especially important if the patient takes metformin 5, 1
• Hypothyroidism-related neuropathy 1
• Consider nerve conduction studies if the diagnosis remains uncertain or if entrapment is suspected 4

Management Strategy

Optimize glycemic control gradually to prevent progression, but avoid rapid HbA1c reduction which can paradoxically worsen neuropathic symptoms 1:

• Target individualized HbA1c based on patient factors 5
• Gradual optimization is key to prevent treatment-induced neuropathy 5, 1

Aggressively manage cardiovascular risk factors since vascular insufficiency drives this condition 1:

• Control blood pressure 1
• Manage lipids aggressively 1

Pain Management if Symptomatic

If neuropathic pain develops, initiate first-line pharmacotherapy immediately with pregabalin, duloxetine, or gabapentin 1:

• Choose based on patient comorbidities, cost, and side effect profile 5
• Do not delay treatment waiting for electrodiagnostic studies 5

Preventive Foot Care Remains Essential

Despite the asymmetric presentation, standard diabetic foot care protocols apply 1:

• Educate on daily foot inspection for cuts, blisters, or pressure areas 1
• Perform annual 10-g monofilament testing to monitor progression and identify areas at risk for ulceration 1
• Arrange podiatry referral for regular foot care 1

Common Pitfall to Avoid

Do not assume all neuropathy in diabetic patients is symmetric distal polyneuropathy - the asymmetric, sequential pattern described here requires recognition of mononeuropathy multiplex as a distinct entity with different underlying pathophysiology requiring more aggressive cardiovascular risk factor management 1, 4.