"Anterior interosseous nerve syndrome (Kiloh Nevin Syndrome) revealing Gantzer muscle and simultaneous myasthenia gravis".

There hasn't been a previous case report of the anterior interosseous nerve injury secondary to the presence of the muscle of Gantzer in a patient with myasthenia gravis in literature before. The anterior interosseous nerve compressive syndrome, also known as Kiloh-Nevin syndrome, is a rare disorder comprising less than 1% of all upper limb neuropathies. Establishing the etiology of anterior interosseous nerve compressive syndrome is challenging because of the lack of specific clinical findings or testing. Herein is the case of a 46 years-old male presented with left eye ptosis, ophthalmoparesis, diplopia, and right-hand weakness. On physical examination, the Pinch Grip test was positive. Electromyography studies showed neurogenic atrophy in the muscles innervated by the anterior interosseous nerve, as well as a pathological decrement of the muscle action potential of more than 10% on repetitive nerve stimulation. Concluding that the presence of the Gantzer muscle caused anterior interosseous nerve compressive syndrome was mainly a diagnosis of exclusion, after careful consideration of other possible etiologies including carpal tunnel syndrome, cervical radiculopathy, and Parsonage-Turner Syndrome. Even though anterior interosseous nerve compressive syndrome is very rare, clinical suspicion ought to arise in the presence of weak radial flexor digitorum profundus and flexor pollicis longus muscles. This case highlights the importance of a thorough medical history, a meticulous physical examination, and particularly the significance of electromyography studies in diagnosing different neuropathological entities. When appropriate, these steps offer information crucial to the differential diagnosis and eventual surgical management, assisting physicians in making informed and accurate treatment decisions.