Myasthenia Gravis is usually worse at which time of day?

• A. In the morning
• B. In the afternoon
• C. End of the day (fatigue)
• D. At night

Answer: (C)

Muscle weakness with myasthenia gravis is fatigable—it gets worse with use and improves with rest. Because muscles accumulate fatigue over the course of the day, weakness tends to be most pronounced later in the day, especially with eye and facial muscles after a day of activity. This diurnal pattern comes from a reduced safety factor at the neuromuscular junction due to autoimmune loss of postsynaptic acetylcholine receptors; as you use the muscles more, transmission becomes increasingly unreliable until rest restores it briefly. So the end of the day is when weakness is usually greatest, rather than in the morning or at night.