Final answer:
Addison's disease causes hyposecretion of cortisol leading to hyperpigmentation of the skin and other symptoms like fatigue and salt cravings, treated with cortisol replacement therapy. In contrast, Cushing's syndrome results from cortisol hypersecretion and has symptoms like obesity and hypertension.
Step-by-step explanation:
Addison's disease is an autoimmune condition that leads to the hyposecretion of cortisol from the adrenal glands. This can manifest as hyperpigmentation, which is a darkening of the skin due to increased melanin, typically in exposed areas and sites of friction. Hyperpigmentation is also accompanied by symptoms such as fatigue, low blood pressure, and cravings for salt due to lost sodium.
Cushing's syndrome, on the other hand, is caused by the hypersecretion of cortisol, often as a result of a pituitary tumor, and features a different set of symptoms including obesity, high blood pressure, and thinning skin with stretch marks.
Melanocyte-Stimulating Hormone (MSH) plays a role in skin pigmentation, with increased production potentially leading to a darkening of the skin. Diagnosis of Addison's disease typically involves blood tests and imaging, and it is treated with lifelong cortisol replacement therapy.