A JAMA Dermatology case report describes progressive slate-grey discolouration of the skin together with darkening of the urine, in a patient with two primary cutaneous melanomas.
Diffuse melanosis cutis with melanuria is rare and it is a sign of widespread metastatic disease rather than a skin problem in its own right: circulating melanin precursors deposit in the dermis and are excreted, which is why the urine darkens on standing. It is easy to mistake for a drug-induced pigmentation - minocycline, amiodarone, chemotherapy agents - or to attribute to hyperpigmentation from another cause, and the delay that follows costs time in a patient who has very little.
The practical value of a case report like this is recognition, and nothing more. A patient with known melanoma who develops generalised grey-blue discolouration needs urgent restaging, not a pigmentation work-up. Asking the patient to leave a urine sample standing for a few minutes is a bedside observation that costs nothing.
- In a patient with known melanoma, treat new generalised slate-grey discolouration as a sign of disease burden until proven otherwise
- Ask about urine colour and look at a sample left to stand
- Review the drug chart for the common causes of diffuse pigmentation before settling on either answer
- Escalate to restaging rather than to a pigmentation work-up
- Remember that more than one primary melanoma raises the index of suspicion further
Why it matters
It is a skin sign that presents to dermatology and belongs to oncology, and the misattribution is to something benign.
Don't overread it
This is a single case report - it describes a presentation to recognise, not a frequency or a prognosis.
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