first consideration is to whether the symptoms due to the statin?
many patients who develop significant weakness and pain on statin therapy have normal CK levels (1)
first objective is to determine the likelihood that the muscle complaint is being caused by statin therapy
factors that make statin toxicity more likely must be weighed against any features that are atypical or that favour an alternate diagnosis
final decision about future statin treatment depends on the balance between the expected benefit of statin therapy for each individual and the likelihood that the symptoms are due to statin therapy
findings from the history that implicate statins
often muscle symptoms resolve within 2 weeks of starting statin therapy
if patients have a normal CK level and can tolerate the symptoms, ask them to continue therapy and see if their symptoms resolve with continued use. Symptoms that persist beyond the first 2 weeks of therapy are likely due to the statin
include symmetric burning or pain in the large muscles during exercise that was not present before lipid-lowering therapy
any symptom that reproducibly recurs with statin rechallenge and disappears within 2 weeks of discontinuing therapy is more likely to be caused by the statin
is the patient a vegetarian? A drinker? Taking supplements?
taking a careful history of diet and supplement use is important to find exposures that may increase the risk of statin-related muscle complaints
vegetarians may develop carnitine or vitamin B12 deficiencies
alcohol and vitamin E and other supplements are occasional causes of muscle symptoms falsely attributed to statin therapy
red yeast rice contains lovastatin, which can exacerbate myopathy, especially when taken in conjunction with another statin
physical examination
the examination of patients with possible statin-induced myopathy begins with a general assessment for signs of hypothyroidism or excess alcohol consumption
ankle-brachial indices are used to exclude significant peripheral vascular disease
musculoskeletal examination focuses on muscle atrophy, tone, tenderness and strength but also excludes tendinopathies, arthropathies, and myofascial pain syndromes, which are often confused with muscle pain
investigations
CK level (preferably more than 72 hours after exercise)
vitamin D level
TSH
further laboratory evaluation depends on the findings and will often be directed by specialist advice
other investigations include
FBC, ESR, CRP, anti-Ro and anti-La antibodies, and the myositis panel in patients with elevated CK whose other findings suggest an autoimmune or inflammatory process
serum carnitine levels (free, total, and esterified), fasting serum lactate levels, and serum cortisol in those with findings suggestive of metabolic myopathy
electromyography and nerve conduction studies in patients with possible myelopathy, peripheral neuropathy, or inflammatory myopathy
muscle biopsy may be necessary to exclude inflammatory or necrotizing myopathies in patients whose CK remains elevated despite withdrawal of statins
may also be helpful when other findings suggest a metabolic myopathy
if a biopsy is needed, magnetic resonance imaging of the affected limb may identify an affected muscle for biopsy
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