Supplementary Material for: Familial Annular Erythema Effectively Responded to Phototherapy: A Case Report of an Extremely Rare Entity and Literature Review

Background: Familial annular erythema is the inherited form of erythema annular centrifugum, in an autosomal dominant fashion. It is an extremely rare cutaneous condition characterized by asymptomatic or mildly itchy annular, arcuate or polycyclic erythematous plaques that appears few days after birth with no systemic manifestaions. Histopathological features are consistent with erythema annular centrifugum. To this date, only five families have been reported to the literature. Case presentation: Herein, we report a family with three generations of affected individuals. The index patient was a 23-year-old female, presented with mildly itchy non-scaly annular and arcuate erythematous plaques that appread since birth. Her paternal grandmother, father, sister and two male cousins have similar condition. Review of system and laboratory work-up was unremarkable. Skin biopsy showed focal compact orthohyperakeratosis, spongiosis, basal cell degeneration, porminent papillary edema with moderate superficial and deep perivascular eosinophilic infiltrate. The index patient was started on narrowband ultraviolet B therapy and showed complete clearance for at least three months. Conclusion: This extremely rare entity is not known to be associated with other organ involvement, apart from the skin. It poses diagnostic difficulty as it resembles other annular conditions during infancy. The presence of similar cases within her family underscores the genetic component of this condition, warranting further investigation and discussion. Possible effective therapeutic options include phototherapy.