Which of the following symptoms is commonly associated with Addison's disease?

The characteristic symptom commonly associated with Addison's disease is dark pigmented skin. This condition stems from adrenal insufficiency, usually due to damage to the adrenal glands, which leads to an inadequate supply of hormones such as cortisol and aldosterone. The resulting hormonal imbalance triggers an increase in the production of adrenocorticotropic hormone (ACTH) by the pituitary gland. High levels of ACTH can stimulate melanocyte activity, which results in hyperpigmentation, particularly noticeable in areas exposed to friction, such as elbows, knees, and scars.

When evaluating the other options, weight gain and increased appetite are typically not associated with Addison's disease; in contrast, individuals with this condition often experience weight loss and decreased appetite due to a lack of cortisol, which is vital for metabolism. Severe headaches can occur due to various causes, but they are not a hallmark symptom of Addison's disease. Thus, dark pigmented skin remains a defining and observable symptom linked directly to the hormonal dysregulation seen in this adrenal disorder.