Table 1.
Type | Clinical presentation | Incidence/prevalence | Long-term outcome |
---|---|---|---|
Myalgia | Unexplained muscle discomfort without CK elevation, including muscle aches, soreness, stiffness, tenderness and exercise-related cramps.4 The pain is dull, aching, widespread and involves the trunk and proximal muscles. Calf and forearm pain is less common and is usually bilateral. | 1–5% in controlled trials and 11–29% in observational studies4 | Myalgias are generally tolerable but can become debilitating, requiring statin withdrawal. The long-term outcome is favourable. Symptoms improve or full recovery occurs in the majority of patients on cessation of statin therapy; however, the condition can continue beyond 14 months.22 |
Myopathy | Muscle weakness (not due to pain and/or CK elevation). A diagnosis is made by the detection of proximal weakness of grade ≤4/5 and standardised muscle testing with confirmation by electromyography and/or muscle biopsy.4 Other causes of muscle weakness should be excluded. | ≈3%25 | An annual assessment of muscle strength is indicated in patients with minimal symptoms without >3 x ULN CK elevations who elect to remain on statin therapy. Serial assessment in asymptomatic patients is unnecessary.4 Among patients with persistent symptoms after statin withdrawal, 10% have underlying neuromuscular disease.23 |
Myositis | Muscle inflammation (determined by skeletal muscle biopsy and/or magnetic resonance imaging), commonly associated with muscle pain and tenderness.4 | Unknown as it is no longer diagnosed by clinical and CPK criteria | Can be toxic or autoimmune. The former improves with statin discontinuation, whereas in the latter only a few patients improve with drug discontinuation; for the remaining patients, the disease is persistent or progressive despite statin discontinuation.21,23,24 The autoimmune type is associated with anti-HMGCR antibodies and requires immunosuppressive therapy (steroids and/or intravenous immunoglobulin).20 |
Myonecrosis | Elevated muscle enzymes or consistently increased serum CK levels. Muscle injury is graded as mild (>3 x baseline untreated CK levels or age-, race- and gender-adjusted ULN), moderate (≥10 x baseline untreated CK levels or age-, race- and gender-adjusted ULN) or severe (≥50-fold above baseline CK levels or age-, race- and gender-adjusted ULN; consistent with an absolute CK concentration of 10,000 IU/L).4 | Incidence is not well defined as CK levels are not routinely measured | No data available for this pathological entity in its full spectrum. |
Clinical rhabdomyolysis | Severe myonecrosis, with myoglobinuria and/or acute renal failure*.4 | Rare (0.1–8.4/100,000 patients/year)21 | Carries a 7.6% risk of death with 19.8% of patients developing acute renal failure and 17% developing renal dysfunction. There is a 5.2% risk of dialysis in affected patients.19 |
CK = creatine kinase; ULN = upper limit of normal; CPK = creatine phosphokinase; HMGCR = 3-hydroxy-3-methylglutaryl-coenzyme A reductase.
Increased serum creatinine levels of >0.5 mg/dL.4