We report the case of a patient with undifferentiated spondyloarthritis (uSpA) who was successfully treated with abatacept after failing all three available tumour necrosis factor (TNF)α antagonists.

Her disease had begun in 2003 with right buttock pain and asymmetrical peripheral arthritis. Human leukocyte antigen (HLA) typing for the B27 antigen, antibodies to cyclic citrullinated peptide and rheumatoid factor were negative. No erosions were observed on x rays of hands and feet. Since MRI of the sacroiliac joints (SI) showed right sacroiliitis, a diagnosis of uSpA with axial and peripheral joint involvement was made.

During the first 4 years of evolution, the disease was unresponsive to different drugs including non-steroidal anti-inflammatory drugs (NSAIDs), oral and intra-articular steroids, methotrexate (MTX), sulfasalazine, cyclosporine, leflunomide, pamidronate, etanercept, infliximab and adalimumab.

In February 2007, the patient presented with right buttock pain, bilateral Achilles enthesitis, tenderness and swelling of the right sternoclavicular joint, both wrists, second to fifth proximal interphalangeal joints of the left hand, both knees and all right metatarsophalangeal joints. Moreover, she presented tenderness and limitation of her left shoulder, both temporomandibular joints and both hips (tender joint count (TJC) 19, swollen joint count (SJC) 14). Erythrocyte sedimentation rate (ESR) was 45 mm/h (normal level<15 mm/h) and C-reactive protein (CRP) 39 mg/litre (normal level<5 mg/litre). The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score was 9.4 and the Bath Ankylosing Spondylitis Functional Index (BASFI) score was 9.0. Pelvis radiographs showed grade 2 right sacroiliitis. MRI showed bone oedema on the sacral side of the right SI joint (fig 1A). After obtaining patient informed consent, we decided to start intravenous abatacept therapy (750 mg on days 0, 15, 29 and then continued at 4-week intervals) while continuing MTX (15 mg/week) and methylprednisolone (16 mg/day).

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Figure 1 T2-weighted short Tau inversion recovery (STIR) MRI. A. MRI obtained before treatment with abatacept, showing bone oedema on the sacral side of the right sacroiliac joint. B. MRI obtained after 3 months showing the reduction of bone oedema. C. MRI obtained after 9 months of abatacept therapy demonstrating the disappearance of bone oedema and its replacement with bone sclerosis.

In May 2007, right buttock pain and Achilles enthesitis improved. The TJC was 13, SJC 7, BASFI score 6.1, BASDAI score 7.0, ESR 40 mm/h and CRP 25 mg/litre. MRI of the SI joints (fig 1B) showed reduction of bone oedema. Methylprednisolone was tapered to 8 mg/day.

In November 2007, right buttock pain had disappeared and physical examination revealed only mild tenderness of the third to fifth metatarsophalangeal joints of the right foot (TJC 3, SJC 0). The BASFI score was 3.4, BASDAI score 3.8, ESR 31 mm/h and CRP 15 mg/litre. MRI of the SI joints (fig 1C) showed the disappearance of bone oedema in the right SI and its replacement with bone sclerosis. Methylprednisolone was stopped and MTX was tapered to 10 mg/week.

In February 2008, after 12 months of abatacept therapy, the patient was in complete remission (TJC 0, SJC 0) and both ESR and CRP were normalised. During the 12-month period of treatment the patient presented no side effects.

Abatacept has been approved for the management of rheumatoid arthritis.1^–3 There is preliminary evidence that costimulatory modulation could also be effective on the skin manifestations of psoriatic disease which are part of the clinical spectrum of SpA.4 5 The results obtained in our patient suggest that abatacept can also work on the musculoskeletal manifestations of SpA. The drug was efficacious on the clinical symptoms but it was also able to ameliorate the bone oedema of sacroiliitis.

In conclusion, our paper is the first reporting the efficacy of abatacept in SpA and suggests that the drug could be an option for patients failing the TNFα blocking therapy.