Radiological Case of the Month FREE

Figure 1. Radiographic examination showing diffuse nodular and interstitial opacities within the lungs.

Figure 2. Radiographic examination showing diffuse nodular and interstitial opacities within the lungs.

Fever of unknown origin is described as a temperature greater than 38.4°C for 2 or more weeks in the absence of localized findings on physical examination. The differential diagnosis for fever of unknown origin is extensive and includes neoplasia, collagen vascular disease, inflammatory bowel disease, and infections such as osteomyelitis, meningitis, tuberculosis (TB), and human immunodeficiency virus. Initial evaluation for fever of unknown origin will include a complete blood cell count and blood culture, urinalysis and urine culture, erythrocyte sedimentation rate, tuberculin skin test with purified protein derivative (PPD) test, and chest radiograph.^1- 2 A PPD test was performed and gastric aspirates were obtained for acid-fast bacilli. A positive PPD result (12 mm) developed and the acid-fast bacilli stain from a gastric aspirate was positive. A diagnosis of miliary TB with meningitis was made. Six weeks after her initial lumbar puncture, the cerebrospinal fluid culture was positive for Mycobacterium tuberculosis.

Mycobacterium tuberculosis is an aerobic, gram-positive, acid-fast bacillus. Transmission of this organism is from person to person through inhalation of respiratory droplets³; however, transmission through the skin, gastrointestinal tract, mucous membranes, placenta, and by infected amniotic fluid have occurred.⁴ Tuberculosis is either an infection or a disease. Tuberculosis infection is defined by a positive PPD test result without physical findings and a chest radiograph that is either normal or has granulomas or calcifications. Tuberculosis disease is defined by signs, symptoms, and/or radiographic manifestations.⁴ The onset of infection after exposure may be from 2 weeks to several years, with a median time of 3 to 4 weeks. Postpubertal adolescents and children younger than 5 years, especially infants, have the greatest risk of developing TB disease after exposure. All reported cases of pediatric TB infection or disease result from exposure to an infected adult.^4- 7

Manifestations of TB are fever, cough, weight loss, diarrhea, vomiting, night sweats, chills, weakness, lymphadenopathy, hepatomegaly, splenomegaly, respiratory distress, hemoptysis, and meningitis. Laboratory evaluation may include leukocytosis or leukopenia, anemia, and hyponatremia, as well as elevated erythrocyte sedimentation rate and elevated alanine aminotransferase, bilirubin, or alkaline phosphate levels.^4,6,8

Tuberculosis has various radiological manifestations, which include parenchymal granulomas, unifocal or multilobar parenchymal consolidation, lobar or segmental atelectasis, hilar or mediastinal lymphadenopathy, pleural effusion, or miliary parenchymal disease. In infants and children, parenchymal consolidation occurs more frequently in the upper lobes.^3- 6

Primary TB occurs in patients not previously exposed and is the most common form of the disease.^3- 4 The primary lesion may disseminate through lymphatic and venous channels, producing miliary and/or extrapulmonary TB. Miliary TB is defined by its "millet-seed" size of 1- to 2-mm yellowish nodules that are found to be granulomas on histological analysis.⁶ The distribution of nodules is diffuse. Miliary TB usually involves the lungs, liver, bone marrow, kidneys, or spleen, but can affect any organ. In cases of disseminated TB, most patients have radiographic findings of miliary TB.^3- 4

The onset of TB meningitis may be rapid or insidious. It usually occurs in children younger than 4 years. This complication occurs from direct seeding of the meninges by hematogenous spread of organisms. These patients also have abnormal chest radiographic findings.^4- 6 Results of cerebrospinal fluid testing are increased leukocyte count with a predominance of lymphocytes, although early in infection polymorphonucleocytes predominate. The glucose level of the cerebrospinal fluid is reduced while the protein level is elevated.^4- 6 Computed tomographic scans of the brain may be normal or show diffuse edema, tuberculomas (ring-enhancing lesions with or without surrounding edema), or obstructive hydrocephalus.³

Definitive diagnosis of TB is made by isolation of the bacillus in culture. Sputum is the specimen of choice.⁴ Tuberculosis is slow-growing and difficult to culture, but therapy should not be delayed for a child with abnormal physical findings and/or radiographic evidence of the disease. Locating the probable adult source is important; in this case, the aunt had a cough and a positive PPD test result.

The treatment of patients with TB depends on the extent of the disease. This patient was prescribed a 4-drug regimen with corticosteroids, which has been shown to reduce long-term neurological impairment in patients with central nervous system involvement.^4,9- 10

Accepted for publication March 31, 1998.

Reprints: Geoffrey A. Jackman, MD, Pediatric Emergency Medicine, Emory University School of Medicine, Egleston Children's Hospital, 1405 Clifton Rd, Atlanta, GA 30322.