Case Report
An Exceptionally Rare Case of Statin Induced Autoimmune Necrotizing Myopathy treated with Intravenous Immunoglobulin
Introduction
statin induced immune mediated necrotizing myopathy (simnm) is a rare entity characterized by progressive muscle weakness. The usual progression of weakness in simnm often exhibits a gradual improvement, highlighting the imperative need for early initiation of immunosuppressive therapy to mitigate the related risks of morbidity and mortality.
Case presentation
We present a case of 74 years old male with history of hypertension, hyperlipidemia presenting with bilateral lower limb edema and intermittent chest pain. Upon arrival at the emergency department, the patient exhibited stable vitals and was not in acute distress1. Initial assessments revealed elevated troponin and transaminase levels, while an electrocardiogram and echocardiogram showed no signs of ischemia2. Further imaging done with chest computed tomography angiogram ruled out pulmonary embolism and revealed small pericardial cyst3. Elevated liver function tests prompted a creatinine kinase evaluation, resulting in a diagnosis of rhabdomyolysis secondary to statin therapy, indicated by a ck level of 32,400. Throughout the 5-day hospitalization, ck levels gradually decreased from 320,400 to 17,000 with aggressive fluid management4. Thyroid panel was normal. Various consultations were sought, including rheumatology, renal, general surgery, and neurology, with electromyography suggesting a myopathic disorder, likely necrotizing5. A lower extremity muscle biopsy confirmed autoimmune necrotizing myopathy. Treatment involved ivig administration (total of 5 doses), continuous renal follow-up to ensure adequate urine output using iv fluids and diuretics, and cessation of amlodipine due to exacerbating leg swelling. Laboratory assessments revealed elevated anti 3-hydroxy-3-methylglutaryl-coenzyme a (hmg-coa) antibodies, while other panels and tests including anti jo 1, antinuclear antibodies came back negative, metabolic myositis panel all came back within normal limits. Additionally, his serum aldolase levels were elevated, making aldolase deficiency extremely unlikely. Muscle biopsy result confirmed autoimmune necrotizing myopathy. Most likely suspicion was that the combination of the new prescription of amlodipine on top of his statin increased the statins risk of myopathy/muscle injury. Ivig therapy led to a gradual improvement in the patient's condition, with ck levels initially stabilizing before slowly declining (figures 1 and 2).
figure 1. Frozen
h&e showing scattered necrotic and regenerating fibers.
figure 2. Mhc1 ihc shows multifocal sarcolemma staining.
Discussion
statin is one of the commonly prescribed drugs and its side effects of
myopathy is well known. However, diagnosing and treating statin induced immune
mediated necrotizing myopathy remains challenging. A broad suspicion is
warranted whenever there is profound weakness with slow improvement in ck
levels. Immune mediated myopathies are generally treated with immunosuppression
and warrants sooner diagnosis to avert considerable morbidity and mortality.
Our patient had significant improvement with ivig but experienced a gradual
decline in ck levels over several weeks
References
4. mammen
al. Statin-associated autoimmune myopathy. New england j med
2016;374(7):664-669.