A 62-year-old man with poorly controlled type 2 diabetes develops severe pain in the right anterior thigh followed over weeks by visible wasting of the quadriceps and an asymmetric weak knee reflex. Sensation distally is preserved and there is no foot drop. The most likely diagnosis is:

• A Lumbar spinal canal stenosis
• B Diabetic third nerve palsy
• C Chronic inflammatory demyelinating polyneuropathy
• D Diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy) ✓

Explanation

Diabetic amyotrophy is an asymmetric painful proximal neuropathy affecting the femoral distribution, with quadriceps weakness and wasting and loss of the knee jerk, typically in older men with type 2 diabetes; it often improves spontaneously over months. Distal sensory loss distinguishes it from typical distal symmetric polyneuropathy. Cranial mononeuropathy affects extraocular muscles, CIDP is symmetric and demyelinating with proximal and distal weakness, and canal stenosis causes claudication-like symptoms rather than focal muscle wasting.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.