A case of synovitis-acne-pustulosis-hyperostosis-osteitis syndrome with robust peripheral arthritis responding to secukinumab

SAPHO (synovitis-acne-pustulosis-hyperostosis-osteitis) syndrome is a rare autoinflammatory disorder with typical cutaneous manifestations of palmoplantar pustulosis (PPP) and eruptive acne, which may also be combined with psoriasiform rashes [1]. The associated arthropathies primarily affect the axial skeleton, while involvement of peripheral joints is relatively uncommon. We report a clinical case of SAPHO syndrome combined with severe peripheral joint involvement, which resolved after treatment with secukinumab combined with bisphosphonates, with the aim of exploring the potential of peripheral arthritis in SAPHO syndrome, detailing its clinical features, with a view to providing a reference for the diagnosis and treatment. Informed consent to participate in the study and publication was obtained from participant.

A 42-year-old male patient presented with psoriasis-like changes on the scalp, chest, and back 14 years ago, followed by palmoplantar pustulosis on both hands and feet as well as pain in the left wrist joint, some distal interphalangeal joints of the bilateral hands, and bilateral sternoclavicular joints, with gradual involvement of both shoulders. X-ray showed bone erosion of some distal interphalangeal joints (Figure 1A), and MRI showed bone marrow oedema of the second and fourth distal interphalangeal joints of the left hand (Figure 1B). 99mTc-MDP bone scintigraphy showed inflammatory changes in the bilateral sternoclavicular joints, the left shoulder joint, the left wrist joint and the distal interphalangeal joints of both hands (Figure 1C). CT chest (oblique coronal) showed bilateral osteosclerosis and bony erosion of the sternoclavicular joints (Figure 1D). Combined with the above medical history and clinical data, according to the Kahn criteria (revised in 2003), the patient was diagnosed with SAPHO syndrome. After the patient received bisphosphonate (pamidronate disodium injection, 4 mg once daily intravenously for three consecutive days), the pain in the sternoclavicular joints improved significantly, and the improvement of the peripheral joints and rash was not obvious; after the combination of interleukin (IL)-17 antagonist (secukinumab injection, 150 mg administered subcutaneously once weekly), the patient’s peripheral joints pain improved significantly, and the rash on the scalp, chest, and back decreased.

Figure 1.

Radiological images of the patient. (A) X-ray of the hands showed narrowing of some distal interphalangeal joint spaces, roughness of articular surfaces, and uneven bone density (arrowheads). (B) MRI of the left hand revealed marrow oedema of the second and fourth distal interphalangeal joints (arrows). (C) 99mTc-MDP bone scintigraphy showed metabolic exuberance at bilateral sternoclavicular joints, the left shoulder joint, the left wrist joint, and distal interphalangeal joints of both hands, suspicious for inflammatory changes (thin arrows). (D) CT chest (oblique coronal) showed bilateral osteosclerosis and bony erosion of the sternoclavicular joints (long arrows).

SAPHO syndrome is a chronic inflammatory rheumatic disease, clinically regarded by some scholars as a subtype of psoriatic arthritis (PsA). However, SAPHO syndrome primarily affects the anterior chest wall and midshaft bones, whereas PsA is chiefly characterised by peripheral joint involvement [2]. This patient demonstrates significant sternoclavicular joint involvement. Combined with a history of palmoplantar pustulosis, this indicates a possible diagnosis of SAPHO syndrome. Furthermore, the patient exhibits symptoms of peripheral joint involvement and psoriasiform skin lesions. In the absence of a standardized clinical treatment protocol for SAPHO syndrome and given the patient’s overlapping clinical features with PsA, therapy was initiated with an IL-17 antagonist combined with bisphosphonate medication. IL-17 is a key cytokine common to the pathogenesis of both SAPHO syndrome and PsA, and it drives disease progression [3], and treatment targeting IL-17 has been shown to be effective in the bone, joint, and cutaneous manifestations of SAPHO syndrome. Concurrently, clinical practice indicates that IL-17 antagonists yield significant therapeutic benefits for peripheral arthropathies associated with PsA [4]. Secukinumab has been shown to improve disease activity in patients with PsA [5], significantly reducing their pain, phalangitis, enthesitis, and skin involvement [6]. Bisphosphonates inhibit osteoclast activity and bone resorption, and also exert anti-inflammatory effect partly through inhibition of tumor necrosis factor-α, which can effectively improve skeletal lesions in SAPHO syndrome and can be used as a complementary treatment modality in PsA to reduce the inflammatory response.

This article reports a case of SAPHO syndrome with pronounced peripheral joint involvement. Following the addition of secukinumab to bisphosphonate therapy, patients demonstrated marked improvement in peripheral joint and skin lesions. Based on these findings, we propose that the combination of an IL-17 antagonist with bisphosphonates may represent an effective therapeutic approach for SAPHO syndrome complicated by peripheral joint involvement.