Impaired Homeostatic Regulation
As in other organ systems, the normal aging of the endocrine system is characterized by a progressive loss of reserve capacity, resulting in a decreased ability to adapt to changing environmental demands. This loss of homeostatic regulation reflects important alterations in hormonal synthesis, metabolism, and action, but these changes may not be clinically apparent under baseline conditions. In fact, basal plasma concentrations of many hormones and metabolic fuels are essentially unchanged with normal aging. This is illustrated by fasting plasma glucose levels that exhibit little change with normal aging, but after a glucose challenge, glucose levels increase much more in healthy older persons as compared to young adults. In some instances, the function of aging endocrine systems is maintained by compensatory changes in secretion of one hormone to offset the loss of function of another hormone in a feedback system, or to compensate for alterations in metabolic clearance. For example, in many older men with testosterone levels in the normal range, pituitary luteinizing hormone (LH) secretion and serum LH levels are increased (although levels usually remain within the normal range), partially offsetting a reduction in testicular testosterone secretion. However, in other cases, these compensatory mechanisms are inadequate to maintain normal function with aging even under basal conditions. For example, unlike cortisol, adrenal production of aldosterone and dehydroepiandrosterone (DHEA) declines disproportionately to clearance rates with aging, leading to age-related decreases in plasma levels of these hormones even under baseline conditions.
Altered Presentation of Endocrine Diseases
The presenting manifestations of endocrine disorders in older adults are often nonspecific, muted, or atypical. For example, hypothyroidism and hyperthyroidism may present similarly with nonspecific symptoms in older people, such as weight loss, fatigue, weakness, constipation, and depression. Endocrine diseases may also present with signs and symptoms that are classic for older patients yet atypical compared to those commonly observed in younger patients. As illustrations, thyrotoxic older patients may exhibit apathy and depression with psychomotor retardation (“apathetic hyperthyroidism”), and diabetes mellitus may present with hyperosmolar nonketotic state, a classic presentation rarely seen in individuals younger than age 50 years (see Chapters 108 and 109). In addition, with aging, it is increasingly common for illnesses to present without any appreciable symptoms, such as hypothyroidism or hypercalcemia secondary to hyperparathyroidism. Finally, the manifestations of endocrine disease may be altered or masked by coexisting illnesses and medications used to treat comorbidities that commonly occur in older people. For example, exacerbations of congestive heart failure or angina may be precipitated by hyperthyroidism in older patients with preexisting cardiac disease, but practitioners may mistakenly attribute the symptoms to worsening primary cardiac disease rather than to thyrotoxicosis in such patients.
Changes in Diagnostic and Therapeutic Approach
Based on the above discussion, it is clear that a high index of suspicion for endocrine (and other) diseases is required in older patients with nonspecific signs and symptoms or functional ...