Which symptom is most likely in a patient experiencing Cushing's syndrome?

Muscle weakness is a classic symptom associated with Cushing's syndrome, which is caused by chronic exposure to excess glucocorticoids, such as cortisol. Patients often experience muscle weakness, particularly in the proximal muscles, which can lead to difficulties in activities such as climbing stairs or lifting objects. This weakness is related to the catabolic effects of excessive cortisol, which promotes protein breakdown and inhibits muscle protein synthesis.

In contrast, the other symptoms listed do not align with Cushing's syndrome. Weight loss is not typical; rather, patients usually experience significant weight gain due to fat redistribution. Signs of hyperthyroidism, such as increased metabolism and weight loss, are not relevant as Cushing's syndrome is linked to elevated cortisol levels rather than thyroid hormone levels. Finally, patients with Cushing's syndrome typically do not exhibit low blood sugar; rather, they may have elevated blood sugar levels due to cortisol's effects on gluconeogenesis and insulin resistance. Hence, muscle weakness is the most characteristic symptom of Cushing's syndrome.