Nonphoto-exposed initial cutaneous manifestation of lupus after zoster: A case of Wolf's isotopic reaction

LMR: locus minoris resistentiae SLE: systemic lupus erythematosus INTRODUCTION An isotopic reaction describes a novel cutaneous condition occurring in a distribution previously affected by another disease, a dermatologic example of locus minoris resistentiae (LMR). LMR represents a physiologic Achilles heel in the skin in which a congenital or acquired altered defense capacity causes a certain region of skin to be more vulnerable and easily affected by a trigger or new disease than others. Since its initial description in 1995, Wolf’s isotopic reaction has been characterized as a type of isotopic reaction in which a classically nondermatomal skin reaction presents in the same dermatome after an initial pathologic insult of a herpes zoster infection (or other herpes viruses). Multiple cutaneous diseases are reported to arise confined to dermatomes previously affected by these viruses, including malignancies, fungal infections, granulomatous diseases, and connective tissue diseases. Hypotheses such as altered immune environment, neuronal damage, and vulnerable connective tissue have been implicated in the development of this response. In vitro studies found that varicella zoster virus alters gene expression affecting cytokeratins, desmosomes, and proteases in keratinocytes. In addition to keratinocytes, the sensory nerve fibers, which modulate the skin immune response secreting neuromediators such as substance P, vasoactive intestinal peptide and calcitonin geneerelated peptide interact with membrane receptors of immune cells in the skin. Immune dysregulation is supported by comparative patch testing studies in which skin previously affected by herpes viruses responded differently compared with unaffected skin when in contact with an allergen.