Drug-Induced Pigmentation
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Direct answer
Drug-induced pigmentation is darkening of skin, mucosa, nails or teeth caused by a medicine, either through increased melanin or through deposition of drug-derived pigment in the dermis. Minocycline, amiodarone, chlorpromazine, clofazimine and gold each produce a recognisable colour and distribution. Matching the colour, the sites involved and a drug history usually identifies the culprit, and a skin biopsy shows where the pigment sits.
What you must remember
- Minocycline pattern: blue-black or slate-grey pigment in old scars, on the shins and face, and on oral mucosa, caused by drug-iron-melanin complexes in the dermis.
- Amiodarone pattern: blue-grey pigmentation of sun-exposed skin, often accompanied by photosensitivity.
- Chlorpromazine pattern: slate-grey pigmentation of sun-exposed areas, related to the dose and duration of therapy.
- Clofazimine pattern: red to brownish-black colouration from crystals stored in macrophages, dose-related and slow to fade after stopping.
- Gold pattern: blue-grey pigmentation of sun-exposed skin and mucosa, seen with gold salts once used in rheumatoid arthritis.
- Hydroxychloroquine pattern: blue-black pigmentation of the hard palate and gums, and skin darkening in some patients.
- Histology clue: dermal melanophages and drug-melanin deposits point to a drug cause, whereas increased basal melanin suggests a different mechanism.
Reading colour, site and mechanism together
Drug pigmentation questions are solved by matching three things: the colour, the body site and the likely deposit. Most culprits can be separated on these features alone. The table sets out the common drugs in one place.
| Drug | Colour | Typical site | Mechanism |
|---|---|---|---|
| Minocycline | Blue-black, slate | Old scars, face, shins, mucosa | Drug-iron-melanin deposits in dermis |
| Amiodarone | Blue-grey | Sun-exposed skin | Lipofuscin-like drug granules in dermal macrophages |
| Chlorpromazine | Slate-grey | Sun-exposed skin | Dermal deposits, dose-related |
| Clofazimine | Red to brown-black | Diffuse, skin and fat | Crystals within macrophages |
| Gold | Blue-grey | Sun-exposed skin and mucosa | Gold granules in dermis |
Blue-grey or slate pigment on sun-exposed skin points towards amiodarone, chlorpromazine or gold, and the drug history separates them. Blue-black colour in old inflamed sites suggests minocycline, while a generalised reddish colour in a patient on leprosy treatment suggests clofazimine. Most drug pigmentation fades slowly after stopping the drug, and some, such as clofazimine, can take months to years to clear.
Where the exam tries to catch you
Pigmentation questions usually turn on the drug history, the site and the timing of onset.
- Trap: calling all drug pigmentation melanin excess Correct: many drugs deposit pigment in the dermis, which needs a different explanation and a biopsy to confirm.
- Trap: labelling any blue-black scar pigment as minocycline without a history Correct: minocycline fits the picture, but the exam wants the drug history and the site considered together.
- Trap: expecting clofazimine colour to clear within weeks Correct: clofazimine is stored in tissue, so the colour can persist for months to years after stopping.
- Trap: assuming photosensitivity alone identifies amiodarone Correct: sun-exposed blue-grey pigment together with thyroid or lung toxicity points to amiodarone.
Frequently asked questions
Which drug causes blue-black pigmentation of old scars?
Minocycline is the classic drug causing blue-black pigmentation of old scars and sites of previous inflammation. The pigment is a drug-iron-melanin complex deposited in the dermis. Fading after stopping minocycline is slow and may be incomplete.
Why does amiodarone cause blue-grey skin pigmentation?
Amiodarone causes blue-grey pigmentation mainly in sun-exposed skin, through drug-containing lipofuscin-like granules in dermal macrophages. Photosensitivity is a related feature. Thyroid and lung toxicity are important clues that the drug is the cause.
How does clofazimine colour the skin?
Clofazimine colours the skin red to brownish-black because the drug crystallises within macrophages in the dermis and fat. The pigmentation is dose-related, and clofazimine is used in leprosy treatment. Colour fades slowly after the drug is stopped, sometimes over months to years.
Which drug darkens the palate and gums?
Hydroxychloroquine is a classic cause of blue-black pigmentation of the hard palate (minocycline can do the same), and it can also darken the shins, face and nail beds in some patients. Mucosal pigmentation is generally benign. It is a clue to drug exposure, but retinal toxicity is a separate and more serious concern with the same drug.
How is drug-induced pigmentation confirmed?
Confirmation rests on the drug history, the colour and distribution, and a skin biopsy showing where the pigment lies. Dermal drug-melanin deposits or macrophage pigment point to a drug cause. Increased epidermal melanin suggests a different mechanism.