Clinical reasoning: A 34-year-old man with recurrent limb weakness

A 34-year-old healthy man presented with 3 weeks of progressive bilateral arm weakness. He first noticed weakness while combing his hair and getting dressed. His symptoms were preceded by transient paresthesia in all 5 fingertips of both hands. Over the next 2 weeks, his weakness progressed slowly and spread to his forearms and hands. He never felt numbness or tingling in the feet. There was no visual disturbance, dysphagia, dysarthria, or bladder or bowel disturbance. There was no prodromal illness or vaccination. He took no medications and did not drink, smoke, or use drugs. Familial history was unremarkable. His general examination, including supine and erect blood pressure and pulse, was normal. The cranial nerves were intact. Strength was 3/5 in both deltoids and 4/5 in remaining muscles of both upper extremities. Neck flexor, extensor, and bilateral lower extremity muscles demonstrated normal muscle strength. Tendon reflexes were all absent apart from reduced bilateral brachioradialis and left triceps reflexes. Sensory tests with pin, cold, vibration, and proprioception had normal results. The rest of his examination, including gait, was normal. ### Question for consideration: 1. What is your differential diagnosis at this stage? This patient presented with progressive bilateral arm weakness. The sensory symptoms were subjective, minimal, and resolved eventually prior to treatment. Although the pattern of weakness suggests a myopathy, the clinical examination is more consistent with a motor neuropathy. The absence of the reflexes, in particular in the legs which were strong, makes the diagnosis of myopathy unlikely. Patients with Lambert-Eaton myasthenic syndrome (LEMS) can have absent reflexes which may reappear after exercise, but frequently have autonomic symptoms with weakness mainly in the legs. The differential diagnosis of an acute motor neuropathy includes the following1: 1. Idiopathic inflammatory causes such as Guillain-Barre syndrome (GBS), multifocal motor neuropathy (MMN), acute onset chronic inflammatory demyelinating polyneuropathy (CIDP), …