Disclosures: James Liu, MD: No financial relationships or conflicts of interest

Case Diagnosis: Vasculitic tibial mononeuropathy.

Case Description: A 29-year-old female with history of actin-related protein complex subunit 1B gene mutations causing immune dysregulation presented with a 1-year history of progressively worsening “crushing and burning” right foot pain with associated plantarflexion weakness. Electrodiagnostic testing revealed a severe right tibial mononeuropathy localizing to a non-entrapment site. Accordingly, she underwent sural nerve biopsy confirming small vessel vasculitis as the source of the tibial nerve injury. Appropriate immunosuppressive treatment was subsequently started leading to significant pain improvement and discharge home.

Setting: Tertiary care, academic electrodiagnostic laboratory.Assessment/

Results: Nerve conduction studies showed severely decreased right tibial motor amplitude. Needle electromyography showed severe denervation of the right soleus muscle with relative sparing of the medial gastrocnemius and normal short head of the biceps. Taken together, there was evidence of a right tibial mononeuropathy localizing just proximal to innervation of the soleus muscle. Sural nerve biopsy showed a small vessel in the perineurium invaded by mononuclear cells with areas of remote, healed vascular injury, consistent with small vessel vasculitis.

Discussion: Proximal tibial mononeuropathies due to mechanical compression are rare and typically associated with vascular compromise from posterior compartment syndrome. However, this did not fit the patient’s presentation. Furthermore, other recognized tibial entrapment entities such as soleal sling syndrome and tarsal tunnel syndrome are not associated with severe tibial denervation at the level of the soleus muscle. Therefore, non-compressive etiologies of tibial mononeuropathies such as vasculitis had to be considered.

Conclusion: It is important to maintain a high index of suspicion for non-compressive etiologies of tibial mononeuropathies such as vasculitis considering compressive tibial mononeuropathies are rare. Electromyographers serve a critical role in evaluating suspected tibial mononeuropathies to not only confirm diagnosis, but also correlate with the patient’s clinical presentation to guide further work-up and ultimately optimize patient care.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/vasculitic-tibial-mononeuropathy-associated-with-inherited-immune-dysregulation-a-case-report/