The Immunocompromised Elderly

In addition to the immune senescence attributed to aging, many elderly are further immunocompromised by underlying illness. For example, an estimated 20% of people over age 75 have diabetes mellitus,¹⁰³ while 47% of patients with renal failure are over 65 years of age.¹⁰⁴ Even 10% of all AIDS cases diagnosed in the United States occur in people over 50 years of age.¹⁸ Other illnesses common in the  elderly include cirrhosis, multiple myeloma, lymphomas, leukemias, and solid tumors. These patients are at higher risk for all types of infections, including gram-negative bacteremia and sepsis.

There are several febrile syndromes unique to the immunocompromised host. Malignant otitis externa is a life-threatening disease found almost exclusively in the elderly diabetic.¹⁰⁵ Spontaneous bacterial  peritonitis, emphysematous cholecystitis, and fungemia are also more common in the immunocompromised. Given the high mortality associated with these syndromes, any febrile elderly patient with a potentially immunocompromising illness should be considered infected. In the majority of cases, early antibiotics and hospitalization will be appropriate.

Fever Of Unknown Origin

Fever of unknown origin (FUO) is classically defined as temperature higher than 38.3?C on multiple occasions, lasting longer than three weeks without a diagnosis after one week of hospital investigation.¹⁰⁵ In the era of managed care, this has been changed from one week in the hospital to three days or three outpatient visits without a diagnosis.¹⁰⁵ The leading cause of FUO is infectious disease. (See Table 14.) If the patient has a documented FUO, consultation with the primary care provider (PCP) or review of medical records may direct further diagnostic work-up. Many of the results in the FUO evaluation are not readily available to the emergency physician, and follow-up should be facilitated with a PCP. Despite this, some causes of chronic fever, such as intraabdominal abscess, active tuberculosis, and endocarditis, are routinely diagnosed in the ED.



Non-infectious Life-Threatening Causes Of Fever In The Elderly

The vast majority of life-threatening fevers in the elderly are caused by infection. However, there are three dangerous conditions that produce hyperpyrexia that are not caused by microbes. These rare entities include heat stroke, salicylism, and neuroleptic malignant syndrome (NMS). (See Table 15.) Thyroid storm and sympathomimetic overdose are also occasional causes of life-threatening hyperpyrexia.



Altered mental status and high temperatures (usually over 103?F) characterize all of these conditions. While the emergency physician should consider heat stroke, salicylism, and NMS in the confused and febrile senior, sepsis and meningitis are far more common. For this reason, be aggressive with antibiotics in such patients while investigating possible non-infectious etiologies.