A 58-year-old man presents to the clinic because of progressive weakness over the past 9 months. He first noticed difficulty buttoning his shirt and frequent dropping of objects. More recently, he has developed trouble climbing stairs and reports muscle cramps and twitching in his arms. He also reports mild dysarthria and occasional choking on liquids. He denies sensory loss, visual changes, bowel or bladder dysfunction, or cognitive decline. Past medical history is unremarkable. He takes no medications. Family history is negative for neuromuscular disease. He is a former smoker and drinks alcohol occasionally. Vital signs are within normal limits. On physical examination, there is muscle atrophy of the hands with visible fasciculations. Neurologic examination reveals spasticity in the lower extremities, hyperreflexia with bilateral Babinski signs, and decreased strength in both upper and lower extremities. Sensory examination is normal.
A) Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by degeneration of both upper motor neurons (corticospinal tracts) and lower motor neurons (anterior horn cells). Patients present with a combination of upper motor neuron (UMN) signs such as spasticity, hyperreflexia, Babinski sign and lower motor neuron (LMN) signs such as muscle atrophy, fasciculations, weakness without sensory deficits. Bulbar involvement can cause dysarthria and dysphagia. Cognitive function is typically preserved, especially in classic ALS.
Answer choice B: Guillain-Barré syndrome, is incorrect. Guillain-Barré syndrome is an acute, immune-mediated demyelinating polyneuropathy characterized by rapidly progressive ascending weakness and areflexia. Sensory symptoms are common, and UMN signs are absent.
Answer choice C: Myasthenia gravis, is incorrect. Myasthenia gravis presents with fatigable weakness that improves with rest and commonly affects ocular and bulbar muscles. Reflexes and sensation are normal, and UMN signs such as spasticity and Babinski sign are not present.
Answer choice D: Multiple sclerosis, is incorrect. Multiple sclerosis causes central nervous system (CNS) demyelination with neurologic deficits separated in time and space. Sensory symptoms, visual disturbances, and MRI findings of demyelinating plaques are common, and LMN signs such as fasciculations are not typical.
Answer choice E: Spinal muscular atrophy, is incorrect. Spinal muscular atrophy is a genetic disorder presenting in infancy or childhood with degeneration of lower motor neurons only. Upper motor neuron signs are not present, distinguishing it from ALS.
Key Learning Point
Amyotrophic lateral sclerosis causes combined upper and lower motor neuron degeneration with preserved sensation, leading to progressive weakness, fasciculations, spasticity, and eventual respiratory failure.
