This case study examines a 45-year-old man who presented with advanced ulnar innervated intrinsic muscle atrophy in the hand, and clawing of the ring and little fingers. This case is unique due to discovery of an anomalous distal forearm muscle with the spontaneous onset and rapid nature of progressive neuropathic symptoms. Further, this patient demonstrated primarily intrinsic motor deficits and denied any sensory deficits on presentation. At surgery, an anomalous distal forearm muscle was found to be compressing the ulnar nerve. This muscle crossed in an oblique fashion, originating from the volar forearm fascia and inserted into the pisiform and proximal abductor digiti minimi fascia. At 5 months after surgery, the patient's ulnar innervated intrinsic muscle strength was improved but still not normal. This case study details the patient's presentation, assessment, surgical management, and postoperative outcome.