The occurrence of a new unrelated disorder at the site of an already healed disease, most commonly identified as the herpes virus, is known as Wolf's isotopic response12. Here, we describe a unique case of multiple epidermal cysts and milia arising on the healed herpes zoster area of a healthy male patient.

A 57-year-old male patient presented with pruritic grouped erythematous papules on his right shoulder, which had persisted for 3 months. He had a history of being diagnosed with herpes zoster which had presented with a painful vesiculopapular eruption about 4 months previously on the exactly same site. After oral antiviral and analgesic treatment, the pain was reduced, but a slight pruritus arose.

The physical examination revealed multiple, unilaterally and linearly distributed erythematous to skin colored tiny papules with a central black pore on the right anterior shoulder (Fig. 1). We received the patient's consent form about publishing all photographic materials.

A histopathological examination of the shoulder demonstrated a ruptured epidermal cyst lined with stratified squamous epithelium that contained a granular layer (Fig. 2). Due to severe pruritus and inflammation, the patient received three injections of an intra-lesional substance with triamcinolone; after this treatment, the pruritus and clinical features improved significantly.

The skin primarily damaged by viruses could have a secondary unrelated disease. The skin which is physically deformed by the preceding disease could be a factor of the response. However, it is most commonly understood that the affected area has immunological vulnerability due to the preceding diseases. In particular, histological analysis demonstrates that the VZV infection affects the cutaneous nerve fiber, nerve endings and distribution of Langerhans' cell, causing an altered local immune condition3.

Frequently reported isotopic responses were granuloma annulare and other granulomatous reactions. However, there were only 12 cases of comedonic-microcystic reactions, and only one case of an epidermal cyst with a histopathological examination was reported345. The patient had undergone an allogenic renal transplantation 4 years previously, and was taking an immunosuppressive agent. Similar to our case, the patient developed multiple epidermal cysts after the presentation of herpes zoster which had occurred 1 year prior5.

Various hypotheses about the pathogenesis of the epidermal cyst and milia exist. Physical damage and histological inflammation of the skin by herpes zoster and bullous disorders may induce the epidermal cyst and milia. In particular, the use of immunosuppressive drugs may contribute to the development of a cyst more easily by exacerbating the inflammation imbalance and pilosebaceous unit occlusion.

Our case is the second case of an epidermal cyst caused by Wolf's post-herpetic isotopic response, but it is the first case that occurred during a short period in a healthy adult without using of immunosuppressive agents.

The incidence of herpes zoster is increasing every year with an increased lifespan and the use of various immunosuppressive agents. Considering these tendencies, it is also assumed that the isotopic response caused by the herpes zoster would also increase. Based on this case, physicians should keep in mind that multiple epidermal cysts could occur from Wolf's post-herpetic isotopic response in healthy adults.