Epidemiology and Pathophysiology
EAC is an uncommon inflammatory skin condition of unknown cause. Histologically, it resembles pityriasis rosea, having a superficial perivascular lymphocytic infiltrate with moderate epidermal acanthosis.1,2 The primary lesions spread peripherally and clear centrally at a maximum rate of 2 to 5 mm/d. Pruritus is common but not always present.1
Although the cause and exact pathogenesis are unknown, EAC may in some cases be triggered by drugs, bacterial infections (like tuberculosis), fungi, viruses, parasites, autoimmune diseases, neoplasms, liver diseases, and dysproteinemias.1,3 Other hypotheses suggest that it may be a type IV hypersensitivity reaction.1 The mean duration is 11 months, but it can vary from as little as 4 weeks to 34 years.1
Diagnostic Tests
No specific tests are needed to make the diagnosis of EAC. However, it is a good idea to do a KOH prep to rule out tinea corporis or candidiasis. This technique has a sensitivity of 88% and a specificity of 95% for tinea.4 Thus, a positive result is sufficient for diagnosis. Fungal culture may be useful if you believe that the diagnosis is truly fungal but the KOH result is negative.
If physical exam leads to suspicion of underlying disease, it is important to order the appropriate diagnostic lab tests. A few case reports have described EAC as the presenting sign in patients diagnosed with cancer approximately 2 years later.1
Treatment
It is helpful if you can find an underlying disease process because most cases of EAC clear as the underlying disease is treated. Review the current drugs and consider replacing any drug reported to have been associated with EAC: chloroquine, hydroxychloroquine, estrogen, cimetidine, penicillin, salicylates, piroxicam, hydrochlorothiazide, and amitriptyline.1
If you have minimal suspicion for an underlying disease process and no causative drug agent is found, most cases of EAC require no treatment and resolve spontaneously.1 However, if pruritus is significant, treat symptomatically. One option is to start with a topical high-potency steroid ointment twice daily. Use this regimen for 2 weeks, then assess response. If the response is good, you may continue a mid-potency steroid as needed or pulse-dosing of a high-potency steroid on the weekends. The goal is to minimize the itching while also minimizing the side effects associated with long-term steroid treatment. Treat as needed and taper when possible. Steroids may cause resolution of lesions but do not prevent recurrence.
A second option is topical calcipotriol, a topical vitamin D derivative. A recent case report has shown this to be beneficial,2 but this is an off-label indication. To date, no randomized clinical trials have been done to demonstrate the efficacy of any other treatment.
Patient Outcome
A KOH prep and a fungal culture were obtained to confidently rule out tinea. Both results were negative. We decided to order a chest x-ray because of his past history of active tuberculosis; the test result was negative. To investigate for any underlying diseases, we ordered a complete blood count, chemistry panel, and erythrocyte sedimentation rate, which all showed normal results.
We explained the diagnosis of EAC as a chronic condition of unknown cause. Since steroids did not provide any relief for him in the past, we offered the option of using calcipotriol ointment, even though the evidence is only based on 1 case report.2 He chose to try the calcipotriol. We warned the patient to not use paint thinner because inhalation and skin exposure are harmful. The patient agreed to stop using it.
Corresponding author
Richard P. Usatine, MD, University of Texas Health Science Center at San Antonio, Department of Family and Community Medicine, MC 7794, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900. E-mail: usatine@uthscsa.edu.