Review Question - QID 212382

This patient's symmetric flaccid paralysis is highly suggestive of spinal muscular atrophy type 1 (Werdnig Hoffmann syndrome), which is caused by anterior horn cell degeneration.

Spinal muscular atrophy (SMA) type 1 is an autosomal recessive condition due to a survival motor neuron (SMN) 1 deletion on chromosome 5 resulting in anterior horn cell degeneration. This results in flaccid paralysis, diminished/absent deep tendon reflexes, and tongue fasciculations. The upper cranial nerves, such as those that control eye movements and facial expression, are typically spared. However, there is a weakness in the bulbar muscles, which results in a weak cry, poor suck, and poor swallow reflex. This condition can lead to respiratory failure and death by 2 years of age.

Incorrect Answers:
Answer 2: Axonal demyelination is seen in multiple sclerosis, an autoimmune disorder. This patient does not fit the demographics of this condition, which typically affects young adults.

Answer 3: Decreased acetylcholine receptor density is seen in myasthenia gravis, an autoimmune condition where there is an immunologic destruction of acetylcholine receptors. This condition is typically seen in young or elderly patients.

Answer 4: Impaired acetylcholine release is seen in botulism. Botulism is caused by exposure to the toxin, which impairs acetylcholine vesicle exocytosis, which is not suggested in this vignette.

Answer 5: Myonecrosis can be seen in Duchenne muscular dystrophy, which is most commonly caused by a frameshift or nonsense mutation of the dystrophin gene. It is typically seen at 2-3 years of age and boys have proximal muscles before the distal muscles weakness, and affects the lower extremities before the upper extremities. Patients also have Gower sign, where boys use their hands to push themselves to be upright.

Bullet Summary:
Spinal muscular atrophy type 1 (also known as Werdnig Hoffmann syndrome) is an autosomal recessive disorder that results in anterior horn cell degeneration.