A Diagnostic Challenge in Progressive Limb Weakness: A Case of Myasthenia Gravis With Atypical Distal and Cranial Nerve Involvement.

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder commonly characterised by fatigable muscle weakness, often presenting with ocular symptoms and proximal weakness, though atypical presentations can also occur, especially in patients with overlapping autoimmune conditions. Prompt diagnosis is essential to initiate effective treatment and prevent complications. We report a case of a 39-year-old male with type 1 diabetes mellitus (T1DM) who presented with a six-week history of progressive limb weakness, imbalance, and intermittent diplopia. Examination revealed bilateral distal upper limb weakness, a possible fourth left cranial nerve palsy, and generalised areflexia, without fatigable ptosis or bulbar involvement. MRI showed only minor cervical disc protrusions, and initial differential diagnoses included diabetic neuropathy, demyelinating disease, and mononeuritis multiplex. Neurophysiological testing confirmed a neuromuscular junction disorder, and acetylcholine receptor antibodies were significantly elevated, leading to a diagnosis of seropositive generalised MG. The patient was started on pyridostigmine and oral prednisolone, with clinical improvement. Further testing revealed autoimmune thyroiditis, and a CT of the thorax excluded thymoma. This report underscores the importance of recognising atypical presentations of MG, as distal limb weakness is not a usual manifestation and can mimic neuropathic disorders. Colinicians should consider MG as a differential diagnosis in patients with atypical neuropathy to ensure timely evaluation and management.