Abstract
In recent years, an autoantibody directed against the 5′-citosolic nucleotidase1A (cN1A) was identified in the sera of sporadic inclusion body myositis (s-IBM) patients with widely variable sensitivity (33%–76%) and specificity (87%–100%). We assessed the sensitivity/specificity of anti-cN1A antibodies in an Italian cohort of s-IBM patients, searching for a potential correlation with clinical data. We collected clinical data and sera from 62 consecutive s-IBM patients and 62 other inflammatory myopathies patients. Testing for anti-cN1A antibodies was performed using a commercial ELISA. Anti-cN1A antibodies were detected in 23 s-IBM patients, resulting in a sensitivity of 37.1% with a specificity of 96.8%. Positive and negative predictive values were 92.0% and 60.6%, respectively. We did not find significant difference regarding demographic variables, nor quadriceps or finger flexor weakness. Nevertheless, we found that anti-cN1A-positive patients presented significantly lower scores in IBMFRS item 1 (swallowing, p = 0.045) and more frequently reported more severe swallowing problems, expressed as an IBMFRS item 1 score ≤ 2 (p < 0.001). We confirmed the low sensitivity and high specificity of anti-cN1A Ab in s-IBM patients with a high positive predictive value. The presence of anti-CN1A antibodies identified patients with a greater risk of more severe dysphagia.
Highlights
Sporadic inclusion body myositis (s-IBM) is an idiopathic inflammatory myopathy (IIM) with peculiar histological and clinical features that include quadriceps and deep finger flexor weakness and often pharyngeal muscle impairment causing dysphagia [1].Inflammatory infiltrates, mainly comprising CD8+ lymphocytes surrounding non-necrotic muscle fibers, along with degenerative features including autophagic abnormalities, such as eosinophilic inclusions and “rimmed” vacuoles, characterize muscle pathology [2]. sporadic inclusion body myositis (s-IBM) represents the most frequent cause of acquired myopathy after 50 years of age, and clinical onset rarely occurs before the fourth decade of life
The main clinical features of the s-IBM and IIM cohorts are summarized in Tables 1 and 2, respectively
Anti-citosolic nucleotidase1A (cN1A) antibodies have a high specificity to distinguish s-IBM from other IIMs, it can be detected in up to 20% of patients suffering from rheumatological diseases [12]
Summary
Sporadic inclusion body myositis (s-IBM) is an idiopathic inflammatory myopathy (IIM) with peculiar histological and clinical features that include quadriceps and deep finger flexor weakness and often pharyngeal muscle impairment causing dysphagia [1].Inflammatory infiltrates, mainly comprising CD8+ lymphocytes surrounding non-necrotic muscle fibers, along with degenerative features including autophagic abnormalities, such as eosinophilic inclusions and “rimmed” vacuoles, characterize muscle pathology [2]. s-IBM represents the most frequent cause of acquired myopathy after 50 years of age, and clinical onset rarely occurs before the fourth decade of life. Sporadic inclusion body myositis (s-IBM) is an idiopathic inflammatory myopathy (IIM) with peculiar histological and clinical features that include quadriceps and deep finger flexor weakness and often pharyngeal muscle impairment causing dysphagia [1]. Due to the slow progression course and the requirement of specific histopathological and clinical features for a definite diagnosis that can be absent in earlier stages of the disease, s-IBM is frequently misdiagnosed with a mean diagnostic delay of 5 years [3]. Diagnostic criteria simplified the pathological criteria and underlined the importance of specific clinical features allowing an earlier diagnosis [4]. The 2011 ENMC diagnostic criteria are more sensitive but less specific when compared with the more stringent Griggs criteria [1]. The sensitivity of anti-cN1A antibodies in s-IBM significantly varies in different studies, ranging from 33% to 76%, mainly due to different detection methods and cut-off thresholds [9,10,11,12,13,14,15,16,17]
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