Endocrine myopathies

As discussed, endocrine disorders of all types can cause muscle disease, ranging from complaints of cramps and aches to tetraparesis. The muscle illness may be the initial manifestation, such as in thyrotoxic periodic paralysis, or the primary complaint, such as weakness in Cushing's disease. The muscle complaints may be nonspecific (aching and cramps in hypothyroidism) or very specific (thyroid ophthalmopathy). Each endocrinologic disorder tends to produce a certain pattern of muscle dysfunction, but clinical presentations vary. When evaluating a patient with a known endocrine disturbance, one should examine carefully for weakness. Inversely, when examining someone with a presentation of muscle weakness, cramps, or atrophy, a thorough review of systems for endocrinopathies is warranted. Screening for thyroid disease is easily done with TSH and T4 levels. A calcium level in a patient with a history of renal failure will assist in elucidating a parathyroid disturbance. Cushing's disease has an obvious phenotype; when indicated, check for an elevated serum ACTH level to confirm the condition. Any patient taking steroids chronically may develop a steroid myopathy, so new onset (or increased) weakness or fatigue in a steroid-dependent individual should justify an evaluation for steroid myopathy. Replacement of the appropriate hormone (or removing the excessive hormone) usually results in resolution of symptoms. Some of the effects of the diseases may be irreversible, or may be only partially reversible. Hyperparathyroidism, in addition to causing muscle cramps and fatigue, is implicated by some authors as possibly leading to, or causing, motor neuron disease. Steroid myopathy may cause diagnostic confusion because of overlap with underlying muscle disease. The most common muscle manifestations associated with hormonal disturbances are fatigue, appreciable muscle weakness, cramping, and atrophy.