Autoimmune myopathies occur in 9 to 14 per 100,000 people,4 with 6% of patients having anti-HMGCR auto-antibodies.5 Anti-HMGCR myositis is more prevalent in older women, patients with type 2 diabetes, and those with a history of atorvastatin use.3,6 Two-thirds of patients with anti-HMGCR myositis report current or prior statin use, and this increases to more than 90% in those age 50 years or older.5 Anti-HMGCR myositis causes significant muscle weakness that does not resolve with discontinuation of the statin and can occur years after the initiation or discontinuation of statin treatment.6 Cardiac involvement is rare4 but dysphagia is relatively common.7,8 Anti-HMGCR myositis also has a weak association with cancer, most commonly gastrointestinal and lung cancers.4,7
Distinguishing statin-induced myalgias from statin-induced myositis guides management. Statin-induced myalgias are associated with normal or slightly increased CK levels (typically < 1000 U/L) and resolve with discontinuation of the statin; the patient can often tolerate re-challenge with a statin.6 In contrast, CK elevation in patients with statin-induced myositis is typically more than 10,000 U/L6 and requires aggressive treatment with immunomodulatory medications to prevent permanent muscle damage.
Treatment recommendations are supported only by case series, observational studies, and expert opinion. Typical first-line treatment includes induction with high-dose corticosteroids followed by prolonged taper plus a conventional synthetic disease-modifying antirheumatic drug (csDMARD) such as methotrexate, azathioprine, or mycophenolate.4 Maintenance therapy often is achieved with csDMARD therapy for 2 years.4 Severe cases frequently are treated with combination csDMARD therapy (eg, methotrexate and azathioprine or methotrexate and mycophenolate).4 Rituximab and IV immunoglobulin (IVIG) are typically reserved for refractory cases.6 Usual monitoring for relapse includes muscle strength testing on examination and evaluation of trending CK levels.8
Our patient received monthly 2-g/kg IVIG infusions, which led to slow, consistent improvement in her strength and normalization of her CK levels to 181 U/L after 6 months.
THE TAKEAWAY
Anti-HMGCR myositis should be suspected in any patient currently or previously treated with a statin who presents with proximal muscle weakness, myalgias, or an elevated CK level. We suggest early subspecialty consultation to discuss whether antibody testing, EMG, or muscle biopsy are warranted. If anti-HMGCR myositis is confirmed, it is advisable to rule out comorbid malignancy and initiate early combination treatment to minimize relapses and permanent muscle damage.
CORRESPONDENCE
Daniel T. Schoenherr, MD, Family Medicine Residency, National Capital Consortium–Alexander T. Augusta Military Medical Center, 9300 DeWitt Loop, Fort Belvoir, VA 22060; danieltschoenherr@gmail.com