National Board of Chiropractic Examiners (NBCE) Practice Test

Muscle weakness that worsens as the day progresses is most characteristic of which condition?

1. Multiple sclerosis

2. Myasthenia gravis

3. Guillain-Barré syndrome

4. Amyotrophic lateral sclerosis

The correct answer is: Myasthenia gravis

Muscle weakness that worsens as the day progresses is a hallmark feature of myasthenia gravis. This condition is caused by an autoimmune response where antibodies attack the acetylcholine receptors at the neuromuscular junction, interfering with the communication between nerves and muscles. As the day goes on, and with successive muscle use, the efficiency of neurotransmission decreases, leading to increased fatigue and muscle weakness. In this condition, individuals often experience stronger muscle strength in the morning after rest, but as they engage in activities throughout the day, the muscles can become increasingly weak. This characteristic fatigability can affect various muscle groups, including those responsible for eye movements, facial expressions, and limb strength. Other conditions listed typically exhibit different patterns of weakness or symptoms. For example, multiple sclerosis may cause fluctuating symptoms and does not usually present with the specific diurnal pattern of weakness seen in myasthenia gravis. Guillain-Barré syndrome presents with a rapid onset of weakness but is more characterized by ascending weakness rather than a pattern of worsening throughout the day. Amyotrophic lateral sclerosis manifests with progressive weakness over time, but it does not typically show the marked diurnal variation associated with myasthenia gravis.