Muscle Pain and Weakness
Lawrence J. Kagen
Consider the etiology of muscle pain and weakness in several categories.
Important diagnostic considerations should include the following: Is the presentation myopathic? Is the nervous system (central or peripheral) involved? Are there vascular factors to be considered? What medications and genetic, hormonal, or metabolic factors may play a role?
Laboratory testing (e.g., levels of enzymes, myoglobin, and creatinuria) is a useful indicator of the severity of myopathy.
Electromyography (EMG) is useful in distinguishing neurogenic from myopathic etiologies.
Magnetic resonance imaging (MRI) and ultrasonography are helpful in diagnosis, in selection of site for possible biopsy, and in determination of the extent and activity of the disease.
Muscle biopsy generally places the diagnosis of myopathy on its most secure footing.
Symptoms of muscle pain (myalgia) and weakness are commonly encountered in clinical medicine. The history to evaluate these problems in affected patients should include not only the site(s), duration, character, and functional limitations but also the family background, medications taken, and other possible comorbid conditions.
I. Myalgia and weakness can be considered under several etiologic categories
Myopathies. These disorders usually are manifested in proximal musculature and present initially with pain and weakness. Atrophy is generally a late finding. The causes of myopathies are many but an abbreviated list would include:
Inflammatory disorders. Dermatomyositis, polymyositis, inclusion body myositis, other connective tissue disorders, especially scleroderma, and Sjögren’s syndrome. Systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and sarcoidosis may also have myositis as a feature.
Endocrinopathies. Many endocrine disorders affect muscles and their function (see Chapter 55). The most commonly encountered are thyroid diseases and diabetes.
Electrolyte disturbances. Particularly those involving calcium, magnesium, sodium, and potassium.
Medications and toxins. Such as the statin agents, penicillamine, and alcohol. Cocaine use may also lead to myopathy.
Genetic diseases. The muscular dystrophies, particularly facioscapular humeral dystrophy, and the distal myopathies in adults should be considered in this category.
Metabolic disorders. Genetic abnormalities of carbohydrate and lipid metabolism can produce pain and exercise intolerance.
Upper motor neuron diseases. Diseases of the brain such as hemorrhage, infarction, infection, or neoplasm may be the cause of weakness and loss of function. Generally, the severity of involvement, its anatomical location, reflex abnormalities, sensory disturbances, and impaired cerebral function will alert the examiner to abnormalities in this area.
Spinal nerve root disorders. Spinal stenosis causes muscle aching and heaviness, generally of the lower extremities, on exertion and may mimic symptoms of vascular ischemia.
Lower motor neuron disorders. The presence of atrophic, flaccid musculature, with cramps, fasciculations, and loss of deep tendon reflexes characterizes these disorders.
Peripheral neuropathies. Neuropathies of this type usually are associated with sensory loss. Weakness, if present, often begins in distal musculature. Atrophy and loss of deep tendon reflexes occur.
Myoneural junction disorders. Myasthenic syndromes may appear similar to myopathies in many aspects. Ocular or facial involvement and marked fatigue are important characteristics.
Other disorders producing muscle symptoms
Vascular. Ischemia due to arterial disease may cause severe muscle pain, especially with exertion, generally of distal musculature.
Polymyalgia rheumatica. This disorder, usually seen in elderly patients, is characterized by severe, often disabling, muscle and joint pain, stiffness, and soreness in the proximal regions that are particularly worse in the morning. Giant cell arteritis may be associated with this disorder.
Fibromyalgia. This is a disorder of uncertain etiology characterized by muscle pain, fatigue, tenderness, and other manifestations often occurring in the presence of psychological stress.
The reader should be aware that the above listing is presented as an initial step to organize an evaluation of the patient’s symptoms. It is not intended to be a complete list of neurologic and myopathic disorders or their manifestations.
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