Pure Motor Isolated Finger Palsy by Cerebral Infarction: Tips for Diagnosis by Neurological Examination

There are various causes of unilateral finger palsy. Its potential etiologies include peripheral neuropathy, carpal tunnel syndrome, and nerve root disorder due to myelopathy. In addition to them, similar paralysis has been reported in localized lesions of the cerebrum, classically referred to as pseudoperipheral palsy. In this report, we describe a case of an 80-year-old man who developed sudden clumsiness of the right fingers. Neurological examination showed muscle weakness mainly in the 1st and 2nd fingers (Medical Research Council grade 1-4) and normal reflexes in the extremities. The affected muscles were innervated by the median nerve, ulnar nerve, and radial nerve, and their nerve root levels ranged from C6 to T1. All the Phalen's, Tinel's, and flick signs were negative. Diffusion-weighted brain magnetic resonance imaging showed hyperintensity limited in the precentral knob on the left precentral gyrus. The etiology was diagnosed as cardiogenic embolism due to atrial fibrillation. In this report, we provide key findings for diagnosing pure motor isolated finger palsy by cerebral infarction through neurological examination.