A rare case of focal neuropathy: Posterior interosseousneuropathy due to lipoma

The posterior interosseous nerve is a pure motor branch of the radial nerve after passing the supinator muscle. It especially innervates the extensor muscles of fingers in the forearm. Injury of the posterior interosseous nerve is most commonly seen in Monteggia fractures, which results from a combination of ulna fracture and proximal radius head dislocation. Idiopathic-inflammatory disease, impingement of the nerve at supinator muscle, neuralgic amyotrophy, and space-occupying lesions are other non-traumatic causes of posterior interosseous neuropathy (PIN). Motor deficits of finger extensors is the main clinical manifestation in the posterior interosseous nerve injury and sensory loss is never seen. A woman aged 49 years presented due to weakness that began 4 years ago in the right 3rd and 4th fingers, which had spread to other fingers. On neurologic examination, paresis of finger and wrist extensors without sensory loss was detected. The patient underwent surgery due to carpal tunnel syndrome and later, cubital tunnel syndrome because of her symptoms. After the operations, her symptoms did not regress and she was evaluated again by us. With her clinical and electrophysiological findings, PIN was diagnosed and on radiologic imaging, a focal lesion and lipoma was found. A rare cause of PIN due to lipoma was diagnosed and she underwent surgery again. A physiotherapy program was started after the operation but after 5 months, there was no significant regression of paresis. We want to report this case because early diagnosis and treatment is important in regaining motor functions in this rare clinical entity.