What is vitiligo?
Vitiligo is a common pigmentation disorder in which the pigment cells (melanocytes) are destroyed by an autoimmune process. The result is the appearance of slowly increasing white patches, without any change in the skin texture. The white patches of skin are prone to sunburn.
What is drug-induced vitiligo?
Drug-induced vitiligo is similar to the non-drug-induced form of vitiligo and is likely due to a similar autoimmune process. It is also called drug-induced leukoderma.
Who gets drug-induced vitiligo?
Drug-induced vitiligo has similar risk factors to those for non-drug-induced vitiligo. These risk factors include:
- Genetic factors
- Race — all races are affected
- Sex — both men and women are affected equally
- Age — drug-induced vitiligo tends to affect older patients than those seen with non-drug-induced vitiligo.
Affected individuals may also develop other autoimmune disorders — especially Addison disease, autoimmune thyroid disease (both hyperthyroidism and hypothyroidism), diabetes mellitus, pernicious anaemia and alopecia areata.
A previous history of vitiligo can also make a patient more vulnerable to a drug-induced extension of their pigment loss.
What causes drug-induced vitiligo?
The most common causes of drug-induced vitiligo are immune-modulating, biologic or targeted medicines. These medicines include:
- Topical imiquimod
- Interleukin (IL)-2, IL-4, and interferon
- Tumour necrosis factor inhibitors: infliximab, adalimumab, and etanercept
- The programmed death receptor inhibitors, pembrolizumab and nivolumab, used in metastatic melanoma (15% of treated patients develop vitiligo)
- BRAF inhibitors: vemurafenib and dabrafenib
- Tyrosine kinase inhibitors: imatinib and gefitinib.
Rare cases of drug-induced vitiligo have also been reported from:
- Topical diphencyprone and squaric acid
- Antimalarials such as hydroxychloroquine
- Other drugs.
The mechanism of drug-induced vitiligo is uncertain and there are currently autoimmune, neural and cytotoxic theories in relation to this.
What are the clinical features of drug-induced vitiligo?
Drug-induced vitiligo has similar features to non-drug-induced vitiligo, with the exception that it tends to have both a rapid onset and extension. Small confetti-like white macules are common in new body sites. Drug-induced vitiligo results in flat patches of depigmented skin with irregular but defined borders. The areas of the body most likely to be affected are the face, elbows and knees, the backs of hands, and the genitals.
Vitiligo is more visible in dark-skinned people, and it so often causes emotional stress or embarrassment, and reduces the affected individual’s quality of life.
How is drug-induced vitiligo diagnosed?
The diagnosis of drug-induced vitiligo is based on the patient’s history and careful general skin examination. Investigations could include:
- Wood lamp skin examination — a Wood lamp is a hand-held UV lamp that can reveal the extent of depigmentation
- Skin biopsy to confirm the complete loss of melanocytes in affected skin.
How is drug-induced vitiligo treated?
The causative drug is stopped, where possible. Treatment options for drug-induced vitiligo include:
- Cosmetic camouflage and sunscreens
- Excimer laser therapy
- Topical corticosteroids and calcineurin inhibitors
- Skin grafts taken from normally pigmented areas.
What is the outcome for drug-induced vitiligo?
Drug-induced vitiligo usually resolves when the offending drug is discontinued, but the time it takes to happen can vary greatly. Vitiligo is difficult to treat.