Increasing multiple myeloma mortality rates in the elderly: demonstration of increasing dependency with increasing age upon age group population size

Epidemiology of the plasma-cell disorders

This review of the plasma-cell disorders begins with the definition of monoclonal gammopathy of undetermined significance (MGUS). The prevalence of MGUS in white and black populations is described. MGUS is a common finding in the medical practice of all physicians, and thus it is important to both the patient and the physician to determine whether the monoclonal protein remains stable or progresses to multiple myeloma (MM), Waldenström's macroglobulinemia (WM), primary systemic amyloidosis (AL), or a related disorder. The long-term (almost 40 years) follow-up data of 241 patients in the Mayo Clinic population is provided. In a large study of 1384 patients with MGUS from southeastern Minnesota, the risk of progression to MM, WM, AL, or other disorders was approximately 1% per year. Risk factors for progression are provided. The incidence of MM in Olmsted County, Minnesota, remained stable for the 56-year span 1945-2001. The apparent increase in incidence and mortality rates among patients with MM in many studies is due to improved case ascertainment, especially among the elderly. The incidence and mortality rates of MM in the United States and other countries are presented. The major emphasis is on the cause of MM, which is unclear. Exposure to radiation from atomic bombs, therapeutic and diagnostic radiation, and in workers in the nuclear industry field are addressed. Many studies involving agricultural occupations, exposure to benzene, petroleum products, and engine exhaust and other industrial exposures are discussed. Tobacco use, obesity, diet, and alcohol ingestion are all possible causes of MM. Clusters of MM have been noted. Multiple cases of MM have been found in first-degree relatives.

The aging population: implications for the burden of neurologic disease

The aging population has had a significant impact upon the societal burden of several neurologic disorders, such as Alzheimer's disease, primary malignant brain tumor, Parkinson's disease, and amyotrophic lateral sclerosis. The increased burden is the result of more than just the dramatically increasing number of elderly individuals. This profound demographic change in the age structure of populations in developed nations is primarily the result of increasing survival. This differential survival over time, and its corresponding less selective culling effect on the surviving population gene pool, is an additional explanation for the observed increasing frequency of several neurologic diseases associated with senescence.

Differential survival, natural selection, and the manifestation of senescence

Evidence for natural selection is typically sought by searching for changes in organisms over generations (that is, evolution). However, evolution may represent but one biological manifestation of the force of natural selection. Although its evolutionary influence diminishes with aging, natural selection might also impact upon the manifestation of senescence via differential survival. Annual population estimates in the United States from 1951 to 1990 for age groups over 60 years old were analyzed. The rate of increase in the size of these age groups increased with increasing age. Since birth rates in developed countries have declined, this finding is a direct manifestation of differential survival over time. Correspondingly, increasing mortality rates from many disorders associated with senescence have been shown to be correlated with increasing age group population size. These observations suggest that natural selection, via differential survival, has had a demonstrable impact upon manifestation rates of the disorders of senescence.

Changing demographics and neurologic disease in the elderly

Mortality from several neurologic diseases has increased dramatically over the past 4 decades among the elderly in developed countries. This trend usually has been attributed to better case ascertainment in recent years. Corresponding demographic changes in the elderly population in developed nations over this same period, a manifestation of differential survival, are sufficient to have contributed substantially to the observed increasing burden of these neurologic diseases. The selective effect of differential survival on the surviving population gene pool is an additional explanation for the observed increasing burden of several neurologic diseases associated with senescence.