Successful corticosteroid-free management of anti-HMG–CoA reductase immune-mediated necrotizing myopathy with subcutaneous immunoglobulins monotherapy: a case report

BACKGROUND: Given the high rate of cardiovascular comorbidities in anti-HMG-CoA reductase (HMGCR)-immune-mediated necrotizing myopathy (IMNM), a glucocorticosteroids (GC)-free treatment approach remains an appealing strategy. While intravenous immunoglobulins (IVIg) represents an effective therapy in most subgroups of idiopathic inflammatory myositis (IIM), there remains limited evidence supporting the use subcutaneous immunoglobulins (SCIg), a potentially safer, more convenient and cost-effective alternative. CASE PRESENTATION: We present a case of a 68-year-old male of European descent with a 2-year history of progressive proximal bilateral lower extremity weakness. He had been treated for his dyslipidemia with atorvastatin for 2 years, then with rosuvastatin for 2 additional years until discontinued a year before our assessment. His other comorbidities included hypertension and diabetes mellitus type II. Physical examination demonstrated proximal weakness of his bilateral hip flexors and deltoids, and no rash. His creatine kinase (CK) was elevated at 1644 IU/L. Electromyography revealed a generalized myopathic disorder with proximal predominance and muscle biopsy of the right quadriceps showed typical findings of an IMNM. Serum HMG-CoA reductase antibody was positive. Due to accumulating evidence supporting the effectiveness of IVIg in anti-HMGCR-IMNM, even without concomitant GC or other immunosuppressive agent, we opted for a GC-free approach through shared-decision making in light of patient's preference regarding potential GC side effects with his comorbidities. As he lived a considerable distance from any center, where IVIg infusions could be offered, and given the patient was unable to drive himself due to his symptoms we opted for SCIg (0.5 g/kg/week). Within 1 month, his CK decreased and weakness resolved. SCIg monotherapy was tapered over 3 years and this patient remains in remission 7 years after SCIg initiation. The patient did not have any adverse effects related to SCIg use. CONCLUSIONS: To our knowledge, this is the first case report describing a successful corticosteroid-free management of anti-HMGCR immune-mediated necrotizing myopathy using SCIg as monotherapy. This case highlights the potential for steroids-free induction and maintenance strategies in IMNM. Larger studies are required to confirm the effectiveness and safety of SCIg in IMNM and other subtypes of IIM, and to provide guidelines for dosing recommendations.