Reverse isotopic response in 77-year-old with widespread rash across the right thorax
A 77-year-old man presented with a widespread rash across his right thorax that spared an area of skin with a history of 2 days. Herpes zoster infection had formed on the right side of his body across the T3 and T4 dermatomes two weeks before presentation. He further had been treated with valacyclovir for one week. He had started using celecoxib daily ten days before his presentation to treat new-onset back discomfort. On examination, an erythematous eruption coalesced and spared the skin surrounding crusted herpes zoster lesions.
The results of the skin biopsy were consistent with a drug rash, and patch testing revealed celecoxib as the trigger. A reverse isotopic response in a medication rash that spared a healed herpes zoster infection was identified. When a new skin disorder spares the area of skin previously damaged by an unrelated, healed dermatosis, this is known as a reverse isotope response. The mechanism underlying this phenomena is unknown. A course of oral glucocorticoids was started, and the patient was told to stop using celecoxib. The broad rash has entirely disappeared 10 days after starting glucocorticoid treatment.
Reverse isotopic phenomenon
The absence of a skin illness at the site of another unrelated skin disease that has already healed is known as reverse isotopic phenomenon, or isotopic non-response. Sparing occurs when an inflammatory disease heals. The majority of accounts of reverse isotope phenomena show the skin previously affected in herpes zoster being spared.
Skin rash, fever, lymphadenopathy, eosinophilia, and multiorgan involvement describe DRESS syndrome, a rare idiosyncratic medication reaction. Anticonvulsant medicines, allopurinol, minocycline, and antiretroviral drugs such as abacavir are common causes. The pathogenesis is unknown, however it is thought to occur in patients who metabolise medicines and active metabolites slowly. Human Herpesviruses have been linked to a genetic predisposition. This illness is thought to be caused by a cross-reaction of antiviral T lymphocytes with the causative medication.4 However, the preservation of the healed herpes zoster site calls this notion into question.
The rash may be caused by a virus altering the local immune response, however, secondary injury sparing the skin lesion is unknown
The possible explanation for a skin lesion being spared from a secondary injury is unknown. The rash of DRESS may be caused by a virus altering the local immune response or by the generation of Th1 cytokines such as TNF-alpha, IFN-gamma, IL-2, and IL-5.2 It has been revealed that the loss or hypoactivity of Langerhans cells at the location of herpes zoster may play a role in this sparing occurrence. In addition, herpesvirus-infected keratinocytes exhibit lower levels of MHC and ICAM-1, impairing their function as antigen-presenting cells and limiting T cell response, resulting in the DRESS skin rash.
Isotopic non-response must be distinguished from isomorphic non-response, also known as the Renbök phenomena. Both of the aforesaid phenomena spare the site of another unrelated skin illness. This sickness is still present in the Renbök phenomena, but it has been healed in the isotopic non-response.
There have been very few reports of reverse isotopic phenomena in literature. There have been instances of vaccination areas being spared, herpes zoster and burn scar occurring in a variety of disorders such as epidermal necrolysis, erythema multiformae, cutaneous lymphomas, leprosy, and annular elastolytic giant cell granuloma. This is most likely the first instance of reverse isotopic phenomena in DRESS disease.