Peripheral Nerve Biopsy in a Patient with Mononeuritis Multiplex
A 60-year-old man with type 2 diabetes and a 6-month history of painful asymmetric foot drop and sensory loss undergoes sural nerve biopsy. The biopsy shows asymmetric loss of myelinated fibers, axonal degeneration, and a few epineurial perivascular inflammatory infiltrates without necrosis. There is no evidence of vasculitis. Direct immunofluorescence is negative. The patient asks if the biopsy explains his symptoms. You are the neuropathologist signing out the case.
1. What is your diagnosis, and how does it relate to his diabetes?
Read the worked answer
The findings are consistent with a diabetic radiculoplexus neuropathy (diabetic amyotrophy) or a non-vasculitic ischemic neuropathy. The asymmetric fiber loss and axonal degeneration suggest an ischemic or microvascular process. The perivascular inflammation is mild and without necrosis, which does not meet criteria for vasculitis. In the context of diabetes, this pattern is typical of diabetic lumbosacral radiculoplexus neuropathy, which is often painful and asymmetric. The biopsy does not show vasculitis, so immunosuppression is not indicated. The neuropathologist should communicate that the findings support a diabetic microvascular etiology and recommend clinical correlation.
2. What pitfalls should be avoided in interpreting this biopsy?
Read the worked answer
Pitfalls include overinterpreting mild perivascular inflammation as vasculitis, which could lead to unnecessary immunosuppression. Also, the presence of axonal degeneration is nonspecific and can be seen in many neuropathies. The absence of necrosis and negative immunofluorescence argue against vasculitis. The neuropathologist should note that the biopsy may not be representative and that the diagnosis is clinicopathologic. Additionally, diabetic neuropathy can have varied patterns, and the biopsy should be interpreted in the context of the clinical history and electrodiagnostic studies.