A New Skin Manifestation at the Site of a Previously Healed Dermatosis: A Case of Wolf's Isotopic Response

Wolf's isotopic response (WIR) is an uncommon phenomenon that refers to the occurrence of a new skin condition at the location of a previously healed dermatosis. We describe an unusual manifestation of bacterial furunculosis which arose as an isotopic response following a herpes zoster episode. The initial skin disease in most cases is herpes zoster and the isotopic response is a granulomatous reaction. A 65-year-old female with a history of chronic lymphocytic leukemia (CLL) and currently on chemotherapy regimen presented with a pustular skin rash on the posterior scalp extending to the posterior right neck and shoulder. Prior to this presentation, the patient was treated for three weeks with valacyclovir for herpes zoster infection which improved her skin condition. During the current hospitalization, the patient's wound cultures from the pustule revealed the growth of methicillin-resistant Staphylococcus aureus (MRSA). Although the patient was on immunosuppressive therapy, her white blood cell (WBC) count increased to 9.9 x 10³/μL. After receiving vancomycin and valacyclovir, her cutaneous condition eventually improved. She was transitioned to oral clindamycin and discharged to a rehabilitation facility. This case describes an immunocompromised patient who was treated for herpes zoster, improved after treatment, and then developed MRSA furunculosis at the same site. It is of significance to report such manifestations, especially in immunocompromised patients, as it could be underdiagnosed. It is also important to inquire about the patients' herpes-related medical history because herpes is the most common initial dermatosis reported in the literature. In such cases of suspected WIR, it is vital to obtain a biopsy before starting treatment with antiviral medication to rule out the possibility of malignancy.