Melanosis is a diffuse gray-brown pigmentation of the skin, secondary to melanin excess.
A mild darkening of the skin may be seen with adrenal insufficiency, or with ACTH-producing tumors such as primary tumors of the pituitary gland, or other malignant tumors metastatic to the pituitary gland.
Diffuse melanosis can also be secondary to diffuse metastatic malignant melanoma, where the pigment is secondary to the presence of melanin metabolites in the circulation, tissue macrophages, or to the presence of intracutaneous single cell metastases.
Melanuria is frequently associated.
Urine in these patients is not usually black when voided, but gradually darkens to a deep brown and later a black color when exposed for several hours to the air.
- Melanosis secondary to melanoma indicates a grave prognosis.