Key Clinical Points
Sarcopenia, a condition of reduced muscle mass and strength with functional consequences, is emerging as a common clinical problem in older adults.
Most myopathies tend to present with shoulder and hip girdle weakness.
Inclusion body myositis, a gradual and insidious loss of muscle mass and strength associated with a characteristic histology and normal to mildly elevated muscle enzyme levels, is the most common form of inflammatory myositis in older adults.
Older adults are at risk for multiple drug–induced myopathies including those related to corticosteroids, heavy ethanol use, and lipid-lowering agents.
The contributions made by healthy muscle to maintaining basic metabolic processes and functional status cannot be underestimated. Muscle disease symptoms and myopathies are not uncommon in older adults, and when present magnify the effects of age-related decline in muscle structure, mass, and function. This chapter surveys the more common myopathies seen in older people, highlighting the differences in presentation and/or therapy between older and younger adults. The discussion of these inflammatory and noninflammatory conditions will be based on an overview of the changes that occur in muscle with aging, and how these age-related changes can alter the results of the standard assessments of muscle disease symptoms.
SARCOPENIA AND MUSCULAR DEBILITY WITH AGE
Sarcopenia is a geriatric syndrome, associated with findings common to other such conditions; multiple etiologic factors work through multiple pathogenic pathways, leading to a unified clinical phenotype. The word sarcopenia, from the Greek for loss of flesh, was first coined in 1988 to refer to the intrinsic age-related loss of lean body (muscle) mass. Population estimates of sarcopenia, previously based solely on the measure of relative muscle mass (derived from either anthropometric data or imaging modalities, and defined as appendicular muscle mass in kg/height in m2), calculated its prevalence to be up to 30% of those over 60 years of age and more than 50% in those over 80, with moderate to severe sarcopenia in 45% of older adults.
The definition of sarcopenia continues to evolve, expanding beyond an early characterization based solely on a threshold for low muscle mass—less than 2 standard deviations below that of a healthy young adult—to one that should incorporate the physiologic and functional consequences (loss of strength and/or performance) associated with aging muscle. Loss of muscle strength (“dynapenia”) with age (“presbydynami”) better predicts adverse outcomes and functional loss than does loss of muscle mass. Loss of strength has been linked to impaired functional status, falls, disability, and increased mortality. Impaired strength may lead to immobility, a shared risk factor for multiple common geriatric syndromes which themselves predispose to frailty. Sarcopenia is thus currently defined as the loss of muscle mass and function with age, with function further specified ...