Drop Foot in a Patient with PPA2 Mutation: A Case Report

Case Diagnosis: 27 year-old male with a right-sided drop foot in the setting of an inorganic pyrophosphatase 2 (PPA2) gene mutation.

Case Description or Program Description: The patient presented to the ED with shortness of breath and was found to be in cardiogenic shock. He was determined to have a left ventricular ejection fraction (LVEF) < 15% due to myocarditis in the setting of coronavirus infection and known PPA2 mutation. He was placed on extracorporeal membrane oxygenation (ECMO) and received an orthotropic heart transplant shortly after. In post-op, the patient was unable to dorsiflex his right foot, and PM&R was consulted. Our findings indicated likely common peroneal nerve (CPN) palsy.

Setting: Tertiary care hospital

Assessment/Results: The patient had no palpable contraction of the muscles involved with dorsiflexion or great toe extension, complete loss of light touch sensation along the lateral leg and dorsum of the foot in the superficial peroneal nerve (SPN) and deep peroneal nerve (DPN) distributions. Deep tendon reflexes (DTR) of the patella and achilles were 1 and 0 respectively, but equal bilaterally. 10 days later, he was found to have some palpable contraction when testing dorsiflexion and toe extension, but no improvement in sensation.

Discussion (relevance): The PPA2 mutation, a rare mitochondrial disorder first described in 2016, is associated with sudden cardiac death often triggered by viral infection or alcohol consumption. As with other mitochondrial disorders, patients are susceptible to myopathy and neuropathy. Notably, there have been reported cases of progressive neuropathy and bilateral foot drop in those who have survived past childhood. This is the first case to our knowledge of compressive neuropathy in the setting of PPA2 mutation.

Conclusions: This case adds to the body of knowledge that PPA2 gene mutation can affect peripheral nerves and that providers should be aware of possible increased susceptibility of developing compressive neuropathies in this population and other similar populations.