Classical fever of unknown origin (FUO): current causes in Mexico.

Background: Causes of FUO change according to medical innovations, modifications of social circumstances, and emerging health risks. Aim. To describe the epidemiology of classical FUO, the time and procedures to achieve a definitive diagnosis, and to underline the variables useful in distinguishing FUO categories. Setting. A third-referral center in Mexico City.

Methods: Patients admitted with prolonged fever were evaluated. Clinical charts of patients with classical FUO were assessed; comparisons between classical FUO categories were made.

Results: 45 patients with 44.9 +/- 17.2 years of age, previous fever duration of 51.2 +/- 51.5 days, and 88.9% referred from other hospitals were evaluated. Nineteen patients had infectious causes; eight, neoplastic conditions; 12, inflammatory non-infectious diseases; one had another cause, and five were discharged with no etiologic diagnosis. Age, LDH levels, length of fever, and weight loss greater than 10 kg may be used to classify patients into a definite category.

Conclusions: Classical FUO is an unusual presentation of frequent infectious diseases; SLE is the main cause within the inflammatory non-infectious conditions, and non-Hodgkin's lymphoma is the first cause of cancer. Some clinical and laboratory clues may be used to guide the study work up of patients with classical FUO.