Atypical Overlapping Features Complicating Diagnoses of Dysferlinopathy and Immune-Mediated Necrotizing Myopathy. (P6-8.006)

Abstract

<h3>Objective:</h3> To present overlapping features and atypical characteristics of dysferlinopathy and immune-mediated necrotizing myopathy (IMNM). <h3>Background:</h3> Dysferlinopathy typically presents with early onset progressive muscle weakness that can be proximal or distal. Definitive diagnosis is made with DYSF gene testing. Treatment is supportive. IMNM is an autoimmune inflammatory myopathy that affects older individuals and is often associated with occult malignancy. Aggressive immunotherapy improves outcomes. Muscle biopsy (MBx) reveals inflammatory infiltrates in both conditions. <h3>Design/Methods:</h3> N/A <h3>Results:</h3> <h3>Case 1:</h3> A 35-year-old man presented with subacute progressive limb weakness and elevated creatine phosphokinase (CPK) &gt;8,000 units/L. MBx showed necrotizing myopathy and sarcolemmal C5b-9 staining; dystrophy stains were omitted due to the patient’s age and subacute symptoms. Anti-signal recognition peptide (SRP) and anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibodies and malignancy screen were negative. The patient was initially diagnosed with seronegative IMNM and treated with steroids, methotrexate and IVIG without improvement. He was subsequently diagnosed with dysferlinopathy based on genetic testing showing double heterozygous pathogenic DYSF gene mutations. <h3>Case 2:</h3> An 18-year-old man presented with 3-years of progressive proximal limb weakness associated with Gower’s sign and elevated CPK &gt;10,000 units/L. Broad muscular dystrophy genetic testing was negative. MBx showed necrotizing myopathy and sarcolemmal C5b-9 staining suggestive of IMNM. Anti-SRP and anti-HMGCR antibodies, serum paraneoplastic panel, and malignancy screening with tumor markers, contrasted CT imaging, and scrotal ultrasound were negative. The patient was diagnosed with early-onset seronegative IMNM. CPK improved and symptoms stabilized with prednisone, methotrexate and IVIG therapy. <h3>Conclusions:</h3> Dysferlinopathy and IMNM can have overlapping clinical features and MBx findings. Heightened awareness of atypical features aids in timely diagnosis. Accurate diagnosis of dysferlinopathy based on genetic testing limits further invasive workup and the side effects of ineffective empiric therapy, whereas early diagnosis of IMNM allows for prompt immunotherapy which is shown to improve prognosis. <b>Disclosure:</b> Dr. Stout has nothing to disclose. Dr. Su has nothing to disclose.