A 50 year old male presents with a 3 month history of fatigue and progressive weakness, predominantly affecting the proximal muscles of the arms and legs. There are associated myalgias and arthralgias. He has lost 8kg in the past 2 months. He is having difficulty rising from a seated position or raising his arms to wash his hair. He has noticed difficulty with swallowing, and frequently coughs when drinking liquids. Blood work demonstrates an elevated CK of 1374.
You are concerned that the patient has an inflammatory myopathy, but what other conditions should be considered in the differential of an elevated CK?
There are six general categories to consider in the differential for an elevated CK.
- Toxin or drug-induced myopathies
Some of the agents that cause this include statins, colchicine, antimalarials, AZT and alcohol.
- Neuromuscular disorders
Includes muscular dystrophies, myasthenia gravis, Eaton-Lambert and ALS.
- Metabolic and endocrine disorders
Hypothyroidism is a fairly common source of an elevated CK. Others include hyperthyroidism, acromegaly, Cushing’s disease, Addison’s disease, glycogen storage diseases, disorders of lipid metabolism, and other inherited metabolic abnormalities.
- Infectious myopathies
These can be local or generalized in association with a variety of organisms.
- Rheumatic diseases
In addition to inflammatory myopathies like polymyositis and dermatomyositis, a number of other rheumatologic conditions can include myopathy leading to CK elevations. These include lupus, mixed connective tissue disease, vasculitis and inclusion body myositis.
Muscle injury and rhabdomyolysis can occur as a result of trauma, drugs, seizures, and metabolic disorders.
On some occasions rises in CK are simply incidental. Patients of African descent often have CK values that are above the reference ranges we use. CK values rise following exercise and IM injections. Some rises in CK are idiopathic and do not lead to muscle weakness or other dysfunction.