Kikuchi–Fujimoto disease (KFD) is a rare condition characterized by necrotizing lymphadenitis and fever, often associated with immune dysregulation. Histologically, it features necrotic foci with abundant histiocytes and plasmacytoid dendritic cells but notably lacks neutrophils and eosinophils. Recent evidence reveals a notable prevalence among pediatric patients, who may exhibit distinct features compared to adults. We reported the case of an 11-year-old girl presenting with persistent fever, cervical adenopathy, and a malar rash, leading to a diagnosis of KFD following lymph node biopsy, which revealed non-suppurative necrosis and histiocytic infiltration. Empirical treatment with antivirals and antibiotics was ineffective, but corticosteroid therapy achieved symptom remission. A literature review identified 48 relevant studies involving 386 pediatric cases, with histopathological findings consistent with classical descriptions of KFD. Cutaneous involvement was reported in 11.14% of cases, ranging from maculopapular rashes to lupus-like eruptions. Notable complications included the development of systemic lupus erythematous, Sjögren syndrome, and rare instances of hemophagocytic syndrome or central nervous system involvement. Kikuchi–Fujimoto disease should be considered in the differential diagnosis of pediatric patients presenting with fever and lymphadenopathy, taking into account a higher frequency of cutaneous manifestations in pediatric cases. A skin biopsy may be helpful in diagnosing KFD and provide valuable information regarding the potential risk of developing systemic lupus erythematosus in the future.

Perineal nodular induration (PNI), also known as cyclist's nodule, is an uncommon reactive pseudotumoral lesion related to repetitive mechanical trauma in saddle sports. Although clinically recognized, its histopathologic spectrum remains incompletely characterized. We performed a retrospective dermatopathologic study of 8 cases of PNI independently reviewed by 2 experienced dermatopathologists using conventional microscopy and digital slide imaging. The study included 7 men and 1 woman, with a median age of 48.5 years (range, 34–76 years). All cases showed a poorly circumscribed fibrohyaline proliferation centered within the deep dermis and subcutaneous tissue. Consistent findings included marked stromal hyalinization, rounded hyalinized collagen nodules, septal remodeling, adipose tissue entrapment, low cellularity, bland spindle cells, and vasculolymphatic dilatation. Significant cytologic atypia, mitotic activity, pseudocyst formation, and neural hyperplasia were absent in all cases. Rounded hyalinized collagen nodules were identified in all cases, and although previous reports describe stromal hyalinization and dense collagen deposition, this nodular collagenous pattern has not been specifically emphasized. Immunohistochemical studies, performed in 2 cases, were nonspecific and overlapped with previously reported profiles. Orcein staining, performed in 2 cases, demonstrated marked reduction or near-complete absence of elastic fibers in both specimens. Our findings suggest that PNI exhibits a reproducible fibrohyaline pattern that may facilitate recognition on routine hematoxylin–eosin sections in the appropriate clinicopathologic setting and may reduce the need for ancillary immunohistochemical studies in selected cases.