Clinical features of immune mediated necrotizing myopathy patients in Viet Nam

Introduction and Aims: Immune mediated necrotizing myopathy (IMNM) is a sub-type of inflammatory myopathies (IIM) that presents with significant muscle weakness, elevated creatine kinase (CK) levels and histopathological features of muscle fiber necrosis, with and without myositis specific antibodies. The aims of this study was to clarify clinical characteristics and autoimmune antibodies (Ab) of patients with immune-mediated necrotizing myopathy (IMNM) in Vietnamese patients. Methods: A retrospective, single centre, case-series, describing the clinical manifestations and laboratory profile, including types of muscle specific antibodies in patients with IMNM. Results: 12 consecutive patients with IMNM, 2 male and 10 female were studied. All of our patients had symmetric, predominantly proximal muscle weakness. 10 patients (83.3%) had severe weakness (MRC≤3/5) and mRS ≥ 3. 8 patients (66.7%) had elevated CK levels of more than 1000UI/L. 33.3% had anti- SRP (signal recognition particle) Ab and 25% had anti- HMGCR (3-hydroxy-3-methylglutaryl-coenzyme A reductase) Ab. The proportion of patients with muscle atrophy, neck weakness, dysphagia and dyspnea between anti-SRP and anti-HMGCR groups did not differ significantly (p> 0.05). Severe muscle atrophy was seen in 1 seronegative patient (25%) and 6 seropositive patients (87.5%), p<0.05. No evidence of an underlying malignancy was found in any patient. Half the patients with anti-SRP Ab (n=2) and 66.7% of those with anti-HMGCR Ab (n=2) had severe weakness, with mRS scores 3–5 (p>0.05) even after treatment. 100% (n=4) of seronegative IMNM and 37.5% (n=3) of seropositive IMNM had significant improvement, with mRS scores 1-2 (p<0.05) after treatment. Discussions: Immune-mediated necrotizing myopathy in our series, is associated with SRP Ab in one third and HMGCR Ab in one quarter of patients. We did not find significant difference between these two groups with regards to clinical features, risk of malignancy and lung involvement and response to immunotherapy. Muscle atrophy was more common in seropositive patients and they appeared to respond less well compared to the 4 seronegative patients to immunotherapy.