Azathioprine is an immunosuppressive agent commonly used for treating active thyroid eye disease (TED). Documented side effects include gastrointestinal intolerance, bone marrow suppression, and hepatic toxicity.1 We describe an unusual side effect of Azathioprine treatment.

Case report

A 51-year-old woman was referred for management of active TED. Past medical history included inactive Darier’s disease. Her thyroid function tests were controlled and she stopped smoking following our advice. The active TED was controlled with oral Prednisolone 40 mg. Azathioprine was gradually introduced in the treatment as a steroid-sparing agent with gradual tapering of Prednisolone after ensuring normal thiopurine methyltransferase levels (106 mU/l, normal; 68-150 mU/l).

At Azathioprine 150mg daily, the patient reported sudden reactivation of a florid, brown papulomatomatous rash on her forehead and chest consistent with reactivation of her Darier's disease (Figures 1a and b). Azathioprine was discontinued and she was treated with oral acitretin (retinoid) by dermatologists with complete recovery (Figures 1c and d).

Figure 1
figure 1

Composite pictures showing reactivation of Darier’s disease after commencing Azathioprine treatment (a, b), with resolution following cessation of Azathioprine and treatment with acitretin (c, d).

Full size image

Comment

Darier’s disease or keratosis follicularis is a dermatological condition affecting seborrheic areas of the skin. Patients present with yellow–brown papules, which have a greasy and warty texture. It is an autosomal dominantly inherited disorder that has been associated with mutations in the gene ATP2A2.2

To our knowledge this is the first reported case of reactivation of Darier’s disease, following the use of Azathioprine treatment. Anolik and Rudolph3 describe a case of a transplant patient being treated with azathioprine and prednisolone who developed a papular rash consistent with Darier’s disease; however, the cause was thought to be secondary to scabietic infestation. In our case scabietic infestation was not identified.

Azathioprine is a purine analog and results in a reduced number of leukocytes owing to disruption of DNA and RNA synthesis.4 A specific gene mutation, known to encode for a calcium pump located on the endoplasmic reticulum, has been identified in relation to Darier’s disease.2 The cause for reactivation of Darier’s disease in our patient may be due to Azathioprine’s pharmacological action within the endoplasmic reticulum, stimulating the Darier’s disease process.

We recommend that Azathioprine is avoided in patients with known Darier’s disease.