A young woman presented with seven months of left hip pain and intermittent anterior chest-wall discomfort. Imaging revealed a destructive osteolytic lesion of the left acetabulum and adjacent ilium with intense FDG uptake on PET-CT, marrow edema on MRI, and soft-tissue edema—findings that appropriately placed malignancy, histiocytic disorders, and infection high on the differential. The initial clinical impression therefore prioritized tumor and infection as the most urgent explanations. Radiology and early biopsy data, however, complicated that first impression.
Computed tomography–guided core biopsy showed fibrogranulation tissue and an epithelioid granulomatous inflammatory process with mixed acute and chronic inflammatory cells. Immunohistochemistry was negative for epithelial markers, CD1a, S100, Langerin, ALK, and OCT2, and positive for CD163. Tissue metagenomic next-generation sequencing (mNGS) reported low-confidence Nocardia farcinica, but investigators identified the same organism in the water bath used for slide preparation and peripheral-blood microbial cell-free DNA testing was negative. Repeat operative sampling after partial resection and curettage demonstrated marrow fibrosis with dense chronic inflammatory-cell infiltration dominated by T lymphocytes and CD68-positive histiocytes, and tissue mNGS from that specimen detected no pathogen.
These sequential pathology and microbiology findings shifted the weight of evidence. Reproducible pathogen detection was lacking, morphology did not show cohesive epithelial malignancy, and Langerhans-cell markers remained negative. Taken together, the cumulative data favored chronic sterile osteitis over proven infection or neoplasm.
Early management reflected the initial uncertainty. Denosumab, 120 mg subcutaneously every 4 weeks, was administered as an antiresorptive measure for presumed tumor-like osteolytic destruction and produced only transient symptomatic relief. Empirical intravenous imipenem-cilastatin plus linezolid, followed by oral linezolid and minocycline, was given while infection remained a serious concern; clinical improvement did not persist. When symptoms progressed, the team performed partial resection, curettage, bone grafting, and internal fixation. Operative pathology reinforced a sterile inflammatory pattern, enabling a reframing of the problem toward inflammatory osteitis and away from an active infectious process requiring prolonged antimicrobial therapy.
After infection and malignancy were considered less likely, clinicians started adalimumab, 40 mg every 2 weeks, to treat osteoarticular inflammation. Joint symptoms improved after the first two injections, indicating TNF-driven disease activity. Skin disease, however, emerged rapidly: pustular lesions developed after the first adalimumab injection and progressed to involve scalp, face, trunk, and limbs. Skin biopsy was consistent with granulomatous folliculitis in the context of the evolving SAPHO presentation. Adalimumab was discontinued.
Subsequent therapies included doxycycline, methylprednisolone, and topical fusidic acid with partial MRI improvement, then trials of apremilast and cyclosporine without durable benefit. Upadacitinib, 15 mg daily, improved the pustular eruption clinically, but serial pelvic and spine MRI showed progression of axial inflammatory disease—bilateral sacroiliitis and multiple vertebral-corner lesions, with the T12 lesion most prominent.
Because objective axial osteitis persisted despite partial skin improvement, clinicians escalated therapy to target the IL-17 axis. Secukinumab was administered at 150 mg weekly for five doses, then 150 mg every 2 weeks, with a later maintenance extension to every 3 weeks. Approximately two months after starting secukinumab, MRI demonstrated marked improvement of the T12 vertebral-corner inflammatory lesion. The pustular eruption did not recur during maintenance, gait improved, and clinicians judged that both bone and skin domains showed a more integrated response.
The treatment sequence in this case illustrates how different immunomodulatory agents produced dissociated effects across organ systems: TNF inhibition improved articular pain but provoked pustular skin disease, Janus kinase inhibition improved skin but failed to arrest axial osteitis on imaging, and IL-17A blockade achieved objective radiologic improvement in vertebral inflammation while maintaining skin control.
This case report rests on repeated tissue sampling, serial imaging, and evolving clinical signs rather than a single definitive diagnostic test. The authors reported that mNGS initially suggested Nocardia but that contamination during slide preparation and negative peripheral-blood microbial cell-free DNA testing weakened that finding. The source did not report any reproducible pathogen in subsequent tissue samples. The modified Kahn diagnostic criteria were applied to support a diagnosis of SAPHO syndrome after exclusion of infection, malignancy, and histiocytic disease.
Limitations include the inherent uncertainty of a single-patient case report and the inability to generalize treatment efficacy from one clinical course. The source did not provide randomized or comparative data to quantify how often IL-17A blockade produces comparable axial radiologic responses in SAPHO, nor did it report long-term follow-up beyond the maintenance interval described. Important unanswered clinical questions documented by the authors include whether IL-17A blockade is broadly effective for SAPHO with destructive osteolytic presentations, which patient features predict response, and how best to integrate serial microbiology, pathology, and imaging into time-sensitive decisions about immunosuppression versus prolonged antimicrobial therapy.
The value of this report lies in its sequential diagnostic reasoning: multidisciplinary reassessment, repeat tissue sampling, and targeted escalation of immunomodulation after systematic exclusion of reproducible infection and neoplasm. These concrete steps, rather than any single test, determined management in a case that initially mimicked tumor or chronic infection and later responded on imaging to IL-17A pathway inhibition with secukinumab.