Prolonged fever of unknown cause
A fever without apparent cause that has persisted for >21 days is defined as ‘prolonged fever of unknown cause’. An explanation is found eventu-ally in the majority of cases. One-third of these will be infectious, and the remaining due to other causes, e.g.:
• Rheumatological: juvenile rheumatoid arthritis, systemic lupus eythematosus, rheumatic fever, vasculitis; periodic fever syndromes.
• Drug fever.
• Factitious illness.
A thorough history and examination are required. Also consider other fac-tors such as travel, geography, age, and significant exposures. Appropriate investigations include:
• Blood: FBC, CRP, ESR, LFTs and renal function tests, albumin.
• Serology: CMV, EBV, brucella, and Q fever.
• Culture: at least 3 serial adequate volume blood cultures, urine culture, stool culture, and consider need for lumbar puncture and bone marrow culture.
• Imaging: of sinuses in the older child and CXR.
• Bone scan or MRI: to exclude osteomyelitis.
• Echocardiography: to exclude endocarditis.
• Skin and blood tests: for TB and blood test for HIV after counselling.
• Antibiotics: these are best avoided until a site of infection has been found. However, in many cases they will have been prescribed already. Remember that antibiotics may be the drug agent causing fever. If the child is critically ill then empiric antibiotics are given.
• Antipyretics: these are best avoided during the period of assessment of fever. For example, blood cultures should be taken when the patient is febrile. One can also determine whether there is a specific pattern to the fever.