Fever of unknown origin (FUO) caused by miliary tuberculosis: diagnostic significance of morning temperature spikes.

Miliary or disseminated Mycobacterium tuberculosis continues to be a difficult diagnostic challenge. The clinical signs and symptoms of miliary tuberculosis (TB) depend on the extent and severity of both pulmonary and extrapulmonary organ involvement. When miliary TB presents as a fever of unknown origin (FUO), the diagnosis of miliary TB can be particularly perplexing. Because only 10% to 20% of patients have a history of antecedent TB, the diagnosis of miliary TB often goes unsuspected until suggested by miliary calcifications on the chest x-ray. High-resolution computed tomography of the chest has enhanced the diagnosis of miliary TB. In patients with miliary TB, acid-fast smear positivity for acid-fast bacilli is low in sputum, urine, and cerebrospinal fluid. Traditionally, miliary TB has been diagnosed by demonstrating granulomas in liver or bone marrow specimens. Transbronchial biopsy may be used when liver and bone marrow biopsies are negative. We present a case of FUO due to miliary TB with miliary calcifications on the chest x-ray but with negative liver and bone marrow biopsies. The clinical diagnosis of miliary TB was further enhanced by finding daily morning temperature spikes characteristic of miliary TB. Morning temperature spikes are associated with only 2 other entities, that is, typhoid fever and periarteritis nodosa, which are unlikely to be confused clinically with miliary TB. Although fever curves/patterns are diagnostically unhelpful in many febrile conditions, characteristic fever curves/patterns are most useful in the most diagnostically difficult cases with obceure fevers, particularly FUOs. Clinicians should take care to analyze the fever curves/patterns in such patients, which may provide an important clue to the diagnosis and prompt specific diagnostic testing.