Immunoglobulin G4 sclerosing disease of the spine in a young patient: illustrative case.

backgroundImmunoglobulinG4-related disease (IgG4-RD) is a systemic immune-mediated fibro-inflammatory condition affecting various organs, mimicking other inflammatory or neoplastic processes. Neurological manifestations, although uncommon, are recognized, with hypertrophic pachymeningitis being the most frequent. OBSERVATIONS: This case is notable for several differences. First, the patient's age and sex (23-year-old female) contrasts sharply with the typical demographic of middle-aged to elderly males. Second, while spinal involvement is known, this case highlighted involvement of the vertebral disc alongside vertebral bodies, leading to a discitis/osteomyelitis with a mass effect, which is a less common finding in neurological IgG4-RD. Most critically, the case was uniquely complicated by a superimposed methicillin-sensitive Staphylococcus aureus infection, resulting in a psoas abscess and discitis/osteomyelitis. This transpired after initial improvement with glucocorticoids and subsequent worsening despite rituximab treatment. LESSONS: This case broadens the known spectrum of IgG4-RD, emphasizing its protean manifestations and the importance of considering it across a broader demographic and atypical spinal involvement. It underscores that clinical deterioration in IgG4-RD patients on immunosuppressive therapy necessitates a thorough re-evaluation, ruling out concurrent infections rather than considering primary disease progression or relapse. A comprehensive diagnostic approach, including repeat biopsies and cultures, and a multidisciplinary management, is vital for optimal patient outcomes. https://thejns.org/doi/10.3171/CASE25789.