Physical Therapy Assistant Practice Exam

Which of the following describes the clinical presentation of spinal muscular atrophy?

1. Distal-to-proximal muscle weakness

2. Skeletal muscle fatiguability

3. Emotional instability

4. Asymmetric motor impairments

The correct answer is: Distal-to-proximal muscle weakness

The clinical presentation of spinal muscular atrophy (SMA) is characterized primarily by distal-to-proximal muscle weakness. SMA affects the motor neurons in the spinal cord, leading to progressive muscular atrophy and weakness. This weakness typically begins in the distal muscles, such as those in the hands and feet, and may progress to involve more proximal muscles over time. This pattern is significant because it differentiates SMA from other neuromuscular disorders that may present with symmetrical proximal weakness or different patterns of muscle involvement. In contrast, while skeletal muscle fatiguability, emotional instability, and asymmetric motor impairments can occur in various neuromuscular or neurological conditions, they are not defining or classic symptoms of SMA. Instead, they may relate to other disorders or secondary complications rather than the core presentation of SMA itself. Thus, the choice identifying distal-to-proximal muscle weakness aligns directly with the characteristic neurological and physical findings seen in patients with SMA.