Pneumonia. Pneumonia (non-tuberculosis) is sometimes manifested by prolonged fever and without clinical symptoms. According to McClung, of 99 cases of fever of unknown origin, 4 had pneumonia. According to Pizzo, of 100 with fever of unknown origin, 4 also had pneumonia, 3 of which were younger than 6 years of age. None of the reports provide information on the specific etiology of pneumonia. It would be interesting to know if these children had a symptom like cough.
Cardiac infections. Bacterial endocarditis often occurs with unexplained fever. Less commonly, the cause of fever is myocarditis or pericarditis.
Infections of the nervous system. Infectious diseases of the central nervous system can sometimes manifest as fever of unknown origin. Three cases of meningitis were found in the Pizzo study, 2 cases of partially treated meningitis — in the McClung series. One observation of bacterial meningitis (without reference to previous treatment) and one tuberculous meningitis are given in the Lohr study. You should also think about a possible brain abscess, subdural empyema, or epidural spinal cord abscess, although neurological symptoms should be observed in these diseases.
Intraabdominal infections. Although intra-abdominal abscesses (including retroperitoneal and pelvic) have been noted in only a few cases in a large series of observations of LDL in children, they require serious attention. Mistakes in their diagnosis and treatment can lead to a serious deterioration of the patient’s condition and significant mortality. Liver abscesses are an infrequent but well-known cause of fever of unknown origin in children. Kaplan described 2 such cases, a Balfour – one, and in children with normal immunity. Diagnosis of this condition can be difficult. Clinical symptoms inherent in the pathologists of the abdominal cavity may be completely absent, and blood cultures are sterile. Diagnostic methods of choice are radioisotope scanning of the liver and gallium scintigraphy of the liver. Bacterial hepatitis and bacterial cholangitis are rare causes of fever of unknown origin in children, although bacterial hepatitis can more often occur in neonatal sepsis. Both of these diseases must be borne in mind even in the absence of jaundice.
After operations on the abdominal organs, especially with perforated purulent appendicitis, and sometimes for no apparent reason, subdiaphragmatic, intra-abdominal and pelvic abscesses may develop. These diseases may be associated with chronic osteomyelitis of the pelvic bones or pelvic venous thrombophlebitis. With bacteremia, a perinephralic abscess may occur. At the same time, analyzes and urine cultures give negative results. Even intravenous pyelography in the early stages of the disease can be normal. It is necessary to remember about the possible connection of pelvic infection with sexually transmitted diseases in adolescent girls. With gonococcal infection, perihepatitis (Fitzhugh-Curtis syndrome) may occur. Prostatitis as a cause of fever of unknown origin in teenage boys occurs infrequently. Perrectal abscesses cause fever of unknown origin mainly only in infants and children with leukemia or other diseases that occur with impaired immunity.
The key to the diagnosis of diseases of the abdominal cavity can serve as pathological symptoms outside it. Pleural effusion, pain in the shoulder, pleural pain, lameness, pain during movements in the hip joint, dysuria may be the only manifestation of an intra-abdominal purulent infection. Infection of superficial tissues. Infectious diseases of the skin, muscles or subcutaneous fatty tissue rarely lead to the development of fever of unknown origin, since these tissues are easily accessible for inspection.