---
title: "Interleukin-17A blockade (secukinumab) for FDG-avid osteolytic SAPHO lesion"
id: "frontiers-in-immunology-7-case-report-interleukin-17a-blockade-for-sapho-syndrome-presenting-as-an-fdg"
canonical_url: "https://medichelpline.com/clinical-feed/frontiers-in-immunology-7-case-report-interleukin-17a-blockade-for-sapho-syndrome-presenting-as-an-fdg"
content_type: "clinical_feed_article"
specialty: "Infectious Disease"
source_name: "Frontiers in Immunology"
source_url: "https://www.frontiersin.org/articles/10.3389/fimmu.2026.1988760"
published_at: "2026-10-23T00:00:00.000Z"
evidence_level: "Journal Feed"
license: "CC-BY-NC-4.0 / Informational Use"
---
# Interleukin-17A blockade (secukinumab) for FDG-avid osteolytic SAPHO lesion
## Provenance & Clinical Metadata
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- **Specialty:** [Infectious Disease](https://medichelpline.com/clinical-feed/infectious-disease.md)
- **Primary Source:** Frontiers in Immunology
- **Source URL:** [Original Journal Publication](https://www.frontiersin.org/articles/10.3389/fimmu.2026.1988760)
- **Published At:** 2026-10-23T00:00:00.000Z
- **Evidence Rating:** Journal Feed
## Executive GIST (TL;DR)
- A 27-year-old woman presented with 7 months of progressive left hip pain and intermittent anterior chest-wall pain; imaging revealed an FDG-avid destructive osteolytic lesion of the left acetabulum and adjacent ilium that initially suggested malignancy, histiocytosis, or infection. - Initial core biopsy showed epithelioid granulomatous inflammation with mixed acute and chronic infiltrates; immunohistochemistry was negative for epithelial and Langerhans-cell markers and positive for CD163. - Metagenomic next-generation sequencing (mNGS) of paraffin tissue reported low-confidence Nocardia farcinica, but the same organism was later detected in the water bath used for slide preparation and peripheral-blood microbial cell-free DNA testing was negative. - Empirical antiresorptive therapy with denosumab (120 mg every 4 weeks) gave transient symptom relief; subsequent progression prompted multidisciplinary reassessment and empirical broad-spectrum antibiotics, which did not produce durable improvement. - Operative curettage and fixation produced tissue showing chronic sterile osteomyelitis-like inflammation dominated by T lymphocytes and CD68-positive histiocytes; repeat tissue mNGS detected no pathogen, shifting the working diagnosis toward **SAPHO syndrome**. - Sequential immunomodulatory therapy: adalimumab (40 mg every 2 weeks) improved joint symptoms but provoked widespread pustular dermatitis consistent with granulomatous folliculitis and was stopped; apremilast and cyclosporine were ineffective. - Upadacitinib (15 mg daily) controlled the skin eruption clinically but axial imaging progressed, with bilateral sacroiliitis and vertebral-corner inflammation (notably T12). - **Secukinumab** (150 mg weekly for five doses, then every 2 weeks, later every 3 weeks maintenance) coincided with marked MRI improvement of the T12 vertebral-corner lesion, no recurrence of pustular disease, and gait improvement within ~2 months. - The case emphasizes iterative clinicopathologic reassessment in destructive inflammatory bone disease, the diagnostic pitfall posed by contaminated molecular results, and a therapeutic rationale for targeting the **IL-17A** axis in SAPHO with active axial osteitis and pustular skin disease. - Limitations included absence of a single definitive microbiologic exclusion test at presentation and the inherent uncertainty of single-patient treatment-response inference for broader therapeutic recommendations.
## Clinical Analysis & Structured Key Points
Frontiers | Case Report: Interleukin-17A blockade for SAPHO syndrome presenting as an FDG-avid destructive osteolytic acetabular lesion CASE REPORT article Front. Immunol. , 23 October 2026 Sec. Autoimmune Disorders Volume 17 - 2026 | https://doi.org/10.3389/fimmu.2026.1988760 Published in Frontiers in Immunology Autoimmune Disorders 7 impact factor 11.3 citescore Editor & Reviewers Edited by D V Dr. Venkataramana Kandi Ph.D., MAMS, FAGE, FRCPath (London) Reviewed by H M Haruki Matsumoto A H ANAMITRA HAIT Outline Figures and Tables Figure 1 View in article Figure 2 View in article Figure 3 View in article Table 1 Timeline of the episode of care. View in article CASE REPORT article Front. Immunol. , 23 October 2026 Sec. Autoimmune Disorders Volume 17 - 2026 | https://doi.org/10.3389/fimmu.2026.1988760 Case Report: Interleukin-17A blockade for SAPHO syndrome presenting as an FDG-avid destructive osteolytic acetabular lesion S L Shu Liu 1 † * A W Anning Wang 1 † Y Y Yiming Yuan 1 † X Y Xiaomin Yan 2 X Y Xianfeng Yang 3 Q J Qiong Jiao 4 Z C Zhiyong Chen 5 S W Shiying Wang 1 * 1. Department of Rheumatology and Immunology, Nanjing Drum Tower Hospital, Affiliated Hospital of Medical School, Nanjing University, Nanjing, China 2. Department of Infectious Diseases, Nanjing Drum Tower Hospital, Affiliated Hospital of Medical School, Nanjing University, Nanjing, China 3. Department of Radiology, Nanjing Drum Tower Hospital, Affiliated Hospital of Medical School, Nanjing University, Nanjing, China 4. Department of Pathology, Shanghai Sixth People’s Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China 5. Department of Rheumatology and Immunology, Shanghai Sixth People’s Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China See more Article metrics View details Abstract SAPHO syndrome is an autoinflammatory osteitis disorder that may be misdiagnosed when bone destruction dominates the presentation. We report a 27-year-old woman with 7 months of left hip pain and intermittent anterior chest-wall pain. Imaging revealed an FDG-avid destructive osteolytic lesion in the left acetabulum and adjacent ilium, initially raising concern for malignancy, lymphoma, Langerhans-cell histiocytosis, or infection. Repeated tissue sampling showed chronic sterile osteomyelitis-like inflammation without evidence of malignancy or a reproducible pathogen. The disease evolved with pustular eruption after tumor necrosis factor inhibition, insufficient axial imaging control with Janus kinase inhibition, and marked improvement of a T12 vertebral-corner inflammatory lesion after interleukin-17A blockade with secukinumab. This case highlights the value of longitudinal clinicopathologic reassessment in destructive inflammatory bone disease and suggests that IL-17A blockade may be a rational strategy for SAPHO syndrome with active axial osteitis and pustular inflammation. Introduction SAPHO syndrome, encompassing synovitis, acne, pustulosis, hyperostosis, and osteitis, is a rare disorder that bridges autoinflammatory bone disease, neutrophil-rich skin inflammation, and spondyloarthritis-spectrum disease ( 1 – 4 ). Classic presentations involve the anterior chest wall, spine, sacroiliac joints, or long bones, often with hyperostosis or osteitis. However, the phenotype is heterogeneous, and skin manifestations can be absent at disease onset or appear later during the disease course. This variability makes early recognition difficult, particularly when a solitary destructive bone lesion is the dominant abnormality. An FDG-avid osteolytic lesion in a young adult appropriately triggers evaluation for malignancy, histiocytic disorders, plasma-cell neoplasms, lymphoma, and infection. Yet sterile osteitis in SAPHO syndrome and chronic recurrent multifocal osteomyelitis can also produce marrow edema, cortical destruction, inflammatory histology, and increased metabolic activity. The clinical challenge is not simply naming a rare diagnosis, but repeatedly recalibrating the probability of tumor, infection, and autoinflammatory disease as pathology, microbiology, imaging, treatment response, and new organ manifestations accumulate. SAPHO syndrome is now better understood as an autoinflammatory disorder of the IL-23/IL-17 axis than as a simple infection of bone, and this shift in conceptual framing has practical consequences for diagnosis, for the interpretation of biopsy and molecular microbiology results, and for treatment selection ( 4 , 17 , 19 ). We report a case in which this longitudinal process ultimately supported SAPHO syndrome and guided escalation to IL-17A blockade, and we compare the presentation with previously reported cases of tumor-mimicking osteolytic SAPHO syndrome and review the emerging treatment landscape. Case description A 27-year-old woman was evaluated in the rheumatology clinic because of a 7-month history of left hip pain and intermittent pain in the left upper anterior chest wall near the costochondral region. She had no fever, weight loss, uveitis, inflammatory bowel symptoms, oral-genital ulceration at presentation, or small-joint arthritis. Initial treatment at a community hospital for presumed costochondritis, including nonsteroidal anti-inflammatory and topical analgesic therapy, did not provide meaningful relief. Two months after symptom onset, hip pain worsened. MRI and computed tomography performed elsewhere showed marrow edema in the left acetabulum and adjacent ilium, edema in surrounding soft tissue, and an osteolytic destructive lesion involving cortical bone. PET-CT showed increased FDG uptake at the left acetabular lesion. The initial radiologic differential diagnosis included aggressive tumor, lymphoma, Langerhans-cell histiocytosis, and infection ( Figure 1 ). Figure 1 Initial imaging of the pelvis and left acetabulum. Axial computed tomography showed a destructive osteolytic lesion in the left acetabulum and adjacent ilium (A–C) . FDG PET-CT showed intense uptake at the lesion (D) . Pelvic MRI showed marrow edema and adjacent soft-tissue edema (E, F) . A computed tomography-guided core biopsy showed fibrogranulation tissue and an epithelioid granulomatous inflammatory process with abundant acute and chronic inflammatory-cell infiltration. Immunohistochemical staining was negative for epithelial markers, CD1a, S100, Langerin, ALK, and OCT2, and positive for CD163. Metagenomic next-generation sequencing (mNGS) of paraffin-embedded tissue detected low-confidence Nocardia farcinica; however, the same organism was detected in the water bath used for slide preparation, and peripheral-blood microbial cell-free DNA testing was negative. At that outside-hospital stage, the working diagnosis remained an aggressive osteolytic tumor or tumor-like lesion, with Langerhans-cell histiocytosis or lymphoma still under consideration and no confirmed infection or SAPHO diagnosis. Denosumab, 120 mg subcutaneously every 4 weeks, was therefore administered as antiresorptive treatment for presumed tumor-like osteolytic bone destruction, not as disease-specific therapy for SAPHO syndrome. The treatment was associated with transient symptomatic improvement. After approximately 4 months of denosumab therapy, hip pain worsened again and MRI showed progression of abnormal signal in the left iliac wing, acetabulum, superior pubic ramus, and surrounding soft tissues ( Supplementary Figure 1A ). At the index rheumatology evaluation, multidisciplinary review considered infection, tumor, histiocytic disease, and sterile autoinflammatory osteitis. Given the osteolytic appearance, inflammatory pathology, and uncertain mNGS result, empirical antimicrobial therapy with intravenous imipenem-cilastatin and linezolid was started. After discharge, oral linezolid and minocycline were continued for 14 days. The left hip symptoms did not substantially improve. One month after discharge, partial resection, curettage, bone grafting, and internal fixation of the left acetabular lesion were performed. The operative specimen showed marrow fibrosis with dense chronic inflammatory-cell infiltration, predominantly T lymphocytes, and CD68-positive histiocytes; CD1a, CD20, and Langerin were negative, and tissue mNGS detected no pathogen ( Figure 2 ). These findings shifted the working diagnosis away from neoplasm or proven infection and toward sterile chronic osteitis. The chronological evolution supporting SAPHO syndrome was therefore cumulative: an FDG-avid destructive sterile osteitis-like lesion, anterior chest-wall pain, repeat negative tissue testing for tumor and reproducible pathogens, later pustular disease with granulomatous folliculitis, and subsequent sacroiliitis and vertebral-corner inflammatory lesions. The episode-of-care timeline is detailed in Table 1 . Figure 2 Pathological findings in the acetabular bone-biopsy and operative specimens. Hematoxylin and eosin staining showed fibrogranulation tissue, chronic inflammatory-cell infiltration, and vascular proliferation around bone fragments (A-C) . In the high-power image (C) , arrows indicate proliferating small vessels (red), lymphocytes (black), and plasma cells (blue) within the mixed inflammatory infiltrate. Immunohistochemical staining showed scattered CD3-positive T lymphocytes (D) , no epithelial component on cytokeratin staining (E) , negative EBER in situ hybridization (F) , abundant CD68-positive histiocytes (G) , and no prominent CD20-positive B-cell infiltrate (H) . Table 1 Time point Clinical/imaging findings Intervention or interpretation 7 months before evaluation Left hip pain and intermittent left anterior chest-wall pain began. Community diagnosis of costochondritis; nonsteroidal anti-inflammatory and topical analgesic treatment did not provide meaningful improvement. 5 months before evaluation MRI/CT showed left acetabular and iliac marrow edema, surrounding soft-tissue edema, and osteolytic bone destruction. PET-CT showed increased FDG uptake; tumor, lymphoma, Langerhans-cell histiocytosis, and infection were considered. After initial biopsy Core biopsy showed epithelioid granulomatous inflammation with mixed acute and chronic inflammatory-cell infiltration; CD163 positive; CD1a, S100, Langerin, ALK, OCT2, and epithelial markers negative. Low-confidence Nocardia farcinica was detected in paraffin tissue mNGS, but water-bath contamination and negative peripheral-blood microbial cfDNA weakened causality. Denosumab 120 mg every 4 weeks was given. Index rheumatology evaluation Pain recurred with abnormal pelvic MRI; MDT reviewed infection, tumor, histiocytic disease, and sterile osteitis. Empirical imipenem-cilastatin and linezolid followed by oral linezolid/minocycline did not substantially improve hip symptoms. 1 month after discharge Partial resection, curettage, bone grafting, and internal fixation were performed. Operative pathology showed chronic osteomyelitis-like inflammation dominated by T lymphocytes and CD68-positive histiocytes; tissue mNGS detected no pathogen. SAPHO syndrome was diagnosed. After adalimumab initiation Adalimumab 40 mg every 2 weeks improved joint symptoms initially, but pustular lesions appeared after the first injection and progressively worsened. Skin biopsy supported granulomatous folliculitis in the context of SAPHO syndrome; adalimumab was stopped. Subsequent treatment Apremilast and cyclosporine were ineffective. Upadacitinib 15 mg daily improved the eruption, but pelvic/spine MRI progressed with bilateral sacroiliitis and vertebral-corner lesions, especially T12. Persistent axial osteitis prompted escalation. After secukinumab Secukinumab 150 mg weekly for 5 doses, then every 2 weeks, was started. Approximately 2 months later, T12 MRI inflammation improved markedly, pustular disease did not recur, gait improved, and maintenance dosing was extended to every 3 weeks. Timeline of the episode of care. Diagnostic assessment The final diagnosis was SAPHO syndrome according to the modified Kahn diagnostic criteria, after exclusion of infection, malignancy, and histiocytic disease ( 2 ). The patient fulfilled the criteria through sterile chronic osteitis or osteomyelitis-like bone inflammation, anterior chest-wall involvement, later pustular skin disease, and subsequent axial inflammatory lesions. The diagnosis was not apparent at onset because the dominant presentation was an FDG-avid destructive acetabular lesion rather than the more familiar sternoclavicular hyperostosis. Several alternative diagnoses were considered and sequentially downgraded. Carcinoma and metastatic disease were unlikely because repeated pathology did not show cohesive epithelial malignant cells, epithelial markers were negative, and systemic imaging did not reveal a primary tumor. Lymphoma was not supported by the pathology, immunophenotype, or lack of a prominent clonal B-cell infiltrate. Langerhans-cell histiocytosis was disfavored by negative CD1a, S100, and Langerin staining. Other histiocytic disorders, including Erdheim-Chester disease and Rosai-Dorfman-Destombes disease, were considered because CD68-positive histiocytes were present, but the distribution, morphology, immunophenotype, and subsequent spondyloarthritis-like evolution were not typical ( 7 – 9 ). Infection remained the most important competing diagnosis early in the course. Osteolytic destruction, soft-tissue edema, chronic inflammatory histology, and granulomatous features can occur in bacterial, mycobacterial, or fungal osteomyelitis. However, the evidence for Nocardia infection was not reproducible and was weakened by possible water-bath contamination, negative peripheral-blood microbial cfDNA testing, negative repeat tissue mNGS, absence of a sustained systemic infectious phenotype, and poor response to antimicrobial therapy. Thus, the pathology was interpreted as chronic osteomyelitis-like inflammation rather than proof of active bacterial infection ( 6 ). This distinction was clinically consequential. If the lesion had been interpreted as proven infection, prolonged antimicrobial therapy or repeated debridement could have delayed control of the systemic inflammatory process. Conversely, premature immunosuppression before adequate tissue sampling would have been unsafe because the imaging appearance was destructive and metabolically active. The final diagnosis therefore depended on the cumulative direction of evidence rather than any single feature: the mNGS result became less persuasive after contamination was identified, whereas the sterile inflammatory pattern became more persuasive as chest-wall pain, pustular disease, sacroiliitis, and vertebral lesions emerged. Therapeutic intervention, follow-up, and outcomes After infection and malignancy became less likely, the diagnosis was reframed as SAPHO syndrome, and treatment was redirected toward inflammatory osteitis. Adalimumab, 40 mg subcutaneously every 2 weeks, was started to control osteoarticular inflammation. Joint symptoms improved after the first two injections, suggesting that TNF-related inflammation was active. However, pustular lesions appeared after the first injection and became progressively extensive with continued treatment, involving the scalp, face, trunk, and limbs ( Figures 3A–D ). Skin biopsy showed epidermal hyperplasia, acanthosis, perifollicular lymphocytic inflammation, follicular dilatation, and histiocytic and multinucleated giant-cell deposition, consistent with granulomatous folliculitis in the context of SAPHO syndrome ( Supplementary Figure 2 ). This cutaneous phase developed after the initial bone presentation and further supported the evolving SAPHO-spectrum diagnosis. Adalimumab was discontinued. After treatment with doxycycline, methylprednisolone, and topical fusidic acid, repeat MRI showed partial improvement 3 months after discharge ( Supplementary Figure 1B ). Figure 3 Pustular dermatitis and spinal MRI response during immunomodulatory therapy. Pustular and erythematous lesions progressively involved the scalp, trunk, and limbs after initiation of adalimumab (A–D) . Sagittal fat-suppressed T2-weighted MRI showed an inflammatory lesion at the T12 vertebral-body corner before secukinumab treatment (E) , arrow). Approximately 2 months after secukinumab was started, repeat MRI showed marked improvement of the T12 lesion (F) , arrow). Subsequent treatment with apremilast and cyclosporine was ineffective. During glucocorticoid tapering, MRI showed recurrent progression of marrow and soft-tissue edema ( Supplementary Figure 1C ). The axial inflammatory phenotype became clearer later in the course: upadacitinib, 15 mg daily, improved the eruption clinically, but follow-up pelvic MRI showed progression to bilateral sacroiliitis, more prominent on the left, with irregular articular surfaces, erosions, marrow edema, and fat deposition ( Supplementary Figure 1D ). Spine MRI showed inflammatory lesions at multiple vertebral-body corners, especially T12 ( Supplementary Figure 1E ). Because active axial osteitis persisted despite clinical skin improvement, secukinumab was administered at 150 mg weekly for five doses, followed by 150 mg every 2 weeks. Approximately 2 months after initiation, repeat MRI showed marked improvement of the T12 vertebral-corner inflammatory lesion; the pustular eruption had not recurred, gait had improved, and the maintenance interval was later extended to every 3 weeks ( Figures 3E, F ; Supplementary Figure 1E ). The treatment goal was therefore broadened from analgesia or suppression of skin inflammation to control of objective axial osteitis. This was important because the patient reported symptomatic fluctuations, whereas MRI showed that inflammatory activity persisted despite partial clinical improvement. Serial imaging was used to distinguish active inflammatory lesions from residual structural damage in the acetabulum and sacroiliac joints. The absence of recurrent pustular disease during secukinumab maintenance, together with improved gait and reduced vertebral-corner edema, suggested a more integrated response across skin and bone domains. Discussion This case is distinctive because SAPHO syndrome initially presented as a metabolically active destructive osteolytic acetabular lesion, a pattern that strongly mimicked tumor or chronic infection. The major strength of the diagnostic approach was repeated tissue sampling and longitudinal reassessment rather than reliance on a single test result. The initial biopsy raised infection as a plausible explanation, but the microbiologic signal was discordant and potentially contaminated. The operative specimen provided a second opportunity to reassess the lesion and showed chronic sterile osteomyelitis-like inflammation without a reproducible pathogen or malignancy. Several features of this presentation have been described previously. Kinoshita et al. described a 54-year-old woman with palmoplantar pustulosis in whom a purely osteolytic femoral lesion with intense FDG uptake on PET-CT was attributed to bone metastasis or chronic bacterial osteomyelitis, with the diagnosis established only after needle biopsy showed no malignancy and cultures were negative; notably, the lesion in that case converted from purely osteolytic to osteosclerotic over 15 months, a transition not documented in the present case ( 14 ). Yang et al. reported three patients in whom SAPHO syndrome was initially managed as spinal infection at outside institutions, in whom PET-CT again demonstrated FDG-avid osteolytic or mixed lesions and in whom diagnosis required systematic exclusion of infection and neoplasm ( 15 ). The 164-patient single-center cohort provides useful denominators for comparison: anterior chest-wall pain was present in all patients, only 2.4% were HLA-B27 positive, and skin involvement was absent in a small but non-negligible minority, confirming that a bone-first presentation without skin disease is a recogniz
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