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Systemic lupus erythematosus (SLE) is associated with substantial morbidity and increased mortality. The reported prevalence of SLE in the USA is 6--241 cases per 100,000 inhabitants [1,2], whereas the incidence is 1--7.6 [3,4]. Due to improved detection of milder forms of the disease, the incidence has nearly tripled in the last 40 years [5]. SLE predominantly affects women, particularly during their childbearing years [6]. However, life expectancy increased substantially in the second half of the 20th century with the diagnosis of SLE among older individuals increasing in parallel; in fact, lupus late in life may occur in up to 25% of all patients [7]. As the age at onset has been recognized as having a modifying effect on the clinical manifestations of SLE, late-onset disease is considered a specific SLE patient subset; however, relatively few studies have focused on this patient subgroup. As new studies emerge, some misconceptions (fictions) are being replaced by facts. We are now summarizing the available literature data regarding this SLE patient subset.
Epidemiology of late-onset SLE
The majority of studies have arbitrarily defined SLE as late onset if it is diagnosed at age 50 or beyond [6,8,9]. However, in recent studies a cut-off age of 65 years or even greater has been proposed [10--12], given the increased life expectancy of the general population [101].
The frequency of late-onset SLE among published series ranges from 4 to 25% [7,9,13--16]. This wide range is probably due to the different cut-off ages used in various studies; however, the possible underestimation of the disease in this patient subgroup needs to be considered, as it may be diagnosed as drug-induced SLE, rheumatoid arthritis, polymyalgia rheumatica or vasculitis.
Striking differences between late- and adult-onset SLE have been reported. First, and as noted in Table 1, the female:male sex ratio declines from a 10--11:1 ratio in the younger adult to a 4:1 ratio in the older adult [6,7,10,13,16--30]; however, this has not been uniformly reported in all studies [8,12,31--34]. This drastic reduction has been attributed to the absence of the effect of sex hormones, which is present in the younger patients [35]. Second, a Caucasian predominance has been reported in late-onset lupus in studies involving multi-ethnic groups [17,26,36]. It is not clear why this is, although...