P060 Unmasking myositis in a complex overlap syndrome

Abstract Introduction Primary Sjögren’s Syndrome (pSS) is a chronic autoimmune condition primarily affecting exocrine glands but is also associated with diverse systemic manifestations. Musculoskeletal involvement is common, often in the form of arthralgia or non-specific myalgia; however, true inflammatory myopathy is rare, with an estimated prevalence of approximately 3%. When present, it can indicate more severe systemic disease. Autoantibodies such as anti-Ro (SSA) and anti-La (SSB) are strongly associated with extra-glandular involvement, including myositis, interstitial lung disease, and neuropathies. Recognising this overlap early is crucial, as inflammatory myositis may be reversible with timely immunosuppressive treatment and multidisciplinary care. Case description A 64-year-old female with a 5-year history of pSS (anti-Ro/La positive) presented with a gradual decline in mobility, increasing proximal muscle weakness, myalgia, and progressive dysphagia over six months. Her background included sicca symptoms, arthralgia, and intermittent parotid gland swelling but no prior organ involvement. On examination, she had symmetrical proximal muscle weakness in the upper and lower limbs, but no skin changes suggestive of dermatomyositis. Initial investigations showed only mildly elevated creatine kinase (CK) levels (430 IU/L), normal aldolase, and negative myositis-specific antibodies (including anti-Mi-2, TIF1-γ, and SRP). Despite the subtle laboratory findings, her functional impairment was significant. EMG revealed myopathic changes with fibrillations and short-duration, low-amplitude motor unit potentials. MRI of the thighs showed patchy muscle oedema, consistent with active inflammation. A quadriceps muscle biopsy demonstrated perivascular and endomysial lymphocytic infiltration with fibre necrosis—supporting a diagnosis of autoimmune inflammatory myositis in the context of known pSS. She responded well to oral corticosteroids (prednisolone 0.75 mg/kg), with improvement in muscle strength and resolution of dysphagia. However, symptoms recurred on tapering below 10 mg, prompting the introduction of methotrexate as a steroid-sparing agent. At 6-month follow-up, she remained clinically stable with near-complete functional recovery. This case exemplifies a rare overlap syndrome requiring collaborative input from rheumatology, neurology, and pathology. Discussion While fatigue and myalgia are frequently reported in pSS, inflammatory myositis represents a distinct clinical entity and carries prognostic implications. EULAR and ACR guidelines emphasise the importance of distinguishing non-specific symptoms from true organ involvement to guide immunosuppression. Inflammatory myopathy in primary Sjogren’s may mimic polymyositis, dermatomyositis, or inclusion body myositis (IBM). Of these, IBM is more commonly reported in older adults with Sjögren’s and tends to be refractory to immunosuppressants. Muscle biopsy was crucial in this case to exclude IBM and confirm an inflammatory process amenable to treatment. This patient’s presentation underscores the limitations of serum CK as a sole marker of muscle disease in overlap syndromes; imaging and histopathology often provide more diagnostic clarity. Her relapse on steroid tapering further illustrates the need for early introduction of DMARDs to maintain remission and reduce glucocorticoid burden, aligning with BSR and EULAR treatment strategies for systemic autoimmune myopathies. The overlap between Sjögren’s and inflammatory myositis remains under-recognised, despite mounting evidence that patients with anti-Ro/La positivity are at increased risk of developing myositis and ILD. This case contributes to the growing awareness that extra-glandular complications can emerge years after initial diagnosis, even in previously stable patients. This case also raised the importance of a multidisciplinary approach—rheumatology initiated systemic immunosuppression, neurology provided EMG interpretation, radiology identified MRI changes, and pathology confirmed the diagnosis via biopsy. The collaboration was essential to delivering effective care. Presenting this case aims to stimulate discussion on diagnostic pitfalls, the role of immunological markers in risk stratification, and long-term management of overlap syndromes in rheumatology practice. Key learning points Inflammatory myositis is a rare but clinically significant extra-glandular manifestation of primary Sjögren’s syndrome, occurring in approximately 3% of patients. Its presentation is often subtle and non-specific, with symptoms such as fatigue and myalgia that can lead to delayed diagnosis unless evaluated with a high index of suspicion. While serum creatine kinase (CK) levels are commonly used in initial assessment, mild or borderline elevations do not reliably exclude underlying muscle inflammation. In such cases, advanced imaging modalities like MRI and electrodiagnostic studies, including electromyography (EMG), provide valuable insights into muscle involvement. However, muscle biopsy remains the gold standard for diagnosis, particularly when rare subtypes such as inclusion body myositis are under consideration. The detection of anti-Ro and anti-La autoantibodies further supports the likelihood of systemic involvement in patients with Sjögren’s syndrome, even in the absence of classical features associated with dermatomyositis or polymyositis. These serological markers play a pivotal role in early risk stratification and long-term disease monitoring. Multidisciplinary collaboration is critical in such complex cases; early involvement of rheumatology, neurology, radiology, and pathology teams ensures a comprehensive and timely diagnostic approach, aligning with current EULAR recommendations for managing systemic autoimmune disorders. Management often begins with corticosteroids, which are effective for acute symptom control. However, due to the high risk of relapse during tapering, early initiation of steroid-sparing agents such as methotrexate or azathioprine is essential to achieve sustained disease control and minimize steroid-related complications. Clinical vigilance remains paramount—new neuromuscular symptoms in patients with known autoimmune disease should prompt thorough investigation, even in the absence of overt biochemical abnormalities. This case underscores the importance of recognising and managing autoimmune overlap syndromes and highlights how evolving rheumatologic guidelines can be integrated into practical, multidisciplinary clinical care.