Adult Sibling Cases of Cutaneous Botryomycosis Leading to the Diagnosis of X-Linked Agammaglobulinemia.

BACKGROUND

X-linked agammaglobulinemia (XLA) is a primary immunodeficiency caused by pathogenic variants in the Bruton tyrosine kinase ( BTK ) gene, leading to severe B-cell maturation defects and pan-hypogammaglobulinemia. Botryomycosis is a rare chronic bacterial infection, typically caused by Staphylococcus aureus ( S. aureus ), characterized by suppurative and chronic inflammation and grape-like bacterial clusters in tissue.

CASE PRESENTATION: We report 2 adult male siblings with previously undiagnosed XLA who presented with cutaneous botryomycosis. Case 1, aged 20 years, developed painless perianal nodules and plaques; laboratory tests revealed markedly decreased IgG, IgM, and IgA. Deep tissue cultures grew methicillin-resistant S. aureus , Streptococcus agalactiae , and Peptoniophilus species. Case 2, his elder brother, aged 21 years, had recurrent pneumonia and persistent verrucous nodules on both lower extremities; methicillin-resistant S. aureus was cultured from a localized abscess. Both siblings carried the same BTK pathogenic variant (c.1760T > C; p.Met587Thr). Skin lesions in both patients resolved with systemic antibiotics and subcutaneous immunoglobulin replacement therapy.

HISTOPATHOLOGY: Biopsies revealed chronic inflammation with scattered neutrophils, fibrosis, and capillary proliferation centered on the hair follicle. Follicular infundibulum contained grape-like clusters of cocci, occasionally forming tetrads, without Splendore-Hoeppli phenomenon. The organisms were Gram-positive and nonspecifically Gomori methenamine silver-positive. Immunohistochemistry confirmed S. aureus as the causative pathogen.

CONCLUSIONS

These sibling cases highlight cutaneous botryomycosis as an under-recognized but clinically relevant manifestation of XLA. Awareness of this association can facilitate earlier diagnosis of the underlying immunodeficiency through integration of clinical history, microbiology, immunohistochemistry, and histopathology.