A fever of unknown origins (FUO) is described as febrile disease/illness. It is characterized as the following: A fever greater than 38.3 degree Celsius on several occasions, the duration of the illness lasts for more than 3 weeks, and there is a failure to reach a diagnosis in spite of a weeklong inpatient evaluation. There could be several possible causes of this fever in children and adults. More often than not, a fever with an unknown origin is an atypical appearance of a common illness rather than an unusual illness.
At present, the description of fever of unknown origins includes people who have been diagnosed following at least 2 outpatient visits or 3 days of admission in the hospital. Other categories include:
- Nosocomial fever of unknown origin is found in hospitalized patients who have a fever of 38.3 °C on many occasions. Patients characterized with this type have a cause not known, and whose preliminary cultures are negative after being incubated upon admission. Their diagnosis is unknown even after 3 days of evaluation.
- Neutropenic fever of unknown origins includes patients with fever who have above <1 x 109 Neutrophils, and whose preliminary cultures are also negative. Their diagnosis is also unknown and uncertain after 3 days.
- HIV associated fever of unknown origins includes patients who are HIV positive with a fever for more than 4 weeks as out-patients or 3 days as inpatients. The diagnosis for these cases is also uncertain after 3 days of evaluation where at least 3 days were allowed for the cultures to incubate.
Common Causes of Fever of Unknown Origin
Diagnosing the type of Fever of unknown origins is crucial for a doctor to create a treatment plan. The various causes responsible for FUO could be any of the following:
- Infections- This is the most common cause of FUO. This could include tuberculosis, mononucleosis, Lyme disease, endocarditis and others.
- Malignancy and Neoplasm- This includes lymphoma, leukemia, pancreatic carcinoma, and other cancers and sarcomas.
- Inflammation in the body- This could include lupus, rheumatoid arthritis, inflammatory bowel disease and others. Connective tissue disorders fall under this category. Under this systemic lupus erythematosus, juvenile rheumatoid arthritis could be potential causes.
- Other causes- This could include fever that are caused by drug use or over-use, hepatitis, hyperthyroidism, deep vein thrombosis, sarcoidosis, and other factors that cannot be classified into specific categories.
Almost all cases are unusual presentations of common diseases such as tuberculosis, gallbladder disease, HIV infection, and endocarditis rather than of rare diseases.
In children, almost about 50 percent of cases are caused by viral infections. Autoimmune diseases, cancers and sarcomas, and other miscellaneous diseases make up the rest of the percentage. Other causes may also include drug induced fever, central nervous system dysfunction and a factitious fever. On the other hand, in adults, cancer or sarcomas, and infections are the most common causes for most of the cases of fever of unknown origins. Autoimmune diseases, meanwhile, are responsible for 10 to 20 percent of the cases, in adults.
In 10 percent of adults, the cause of fever of unknown origin is not identified. These other sources of fever of unknown origins could be the following:
- Acquired immunodeficiency syndrome (AIDS)
- Fungal infections
- Parasitic infections
- Systemic bacterial illnesses
- Inherited diseases
- Polymyalgia rheumatica (PMR)
- Endocrine disorders
- Polyarteritis nodosa (PAN)
Diagnosing Fever of Unknown Origins
In most cases FUO resolves itself in time. Once the fever lasts for more than 3 weeks and gets diagnosed as a fever of unknown origins, the doctor will then run some diagnostic tests to find out more on the underlying causes of the fever. Various tests that they will ask you to run include the following:
- The doctor will ask you to describe your medical/health history. He/she could also ask you questions regarding your travel history, if you have been subjected to certain environmental conditions such as excessive smoking etc or if you have had any changes in your daily environment. They could also ask you questions about your family history of illnesses (genetic profile). This could help find out if the underlying cause is a disease such as lymphoma or rheumatic fever.
- Blood tests and physical examination. Blood tests helps check for certain conditions such as autoimmune conditions that might not have very visible or obvious symptoms. During a physical examination the doctor is able to examine your body of rashes, or for signs of certain underlying conditions such as jaundice etc. If your blood tests come out positive, the doctor could also ask you to undergo some more tests to confirm the diagnosis of the underlying cause.
- Apart from blood tests the doctor could ask you to have a urine test and sputum cultures test. This will help check for cause of FUO such as bacteria or fungi. Specific other tests can also help check for viral infections or other infections that might be the underlying cause of FUO.
- Imaging tests also help a doctor diagnose the causes of FUO. X-rays or endocardiogram are some of the tests that a doctor may ask you to get done.
Doctors should be aware of all the symptoms (both previous and present) of the patient by asking them again. This is because even if the assessment of the condition if thorough, patient usually remember other details too when the questions are repeated.
The prognosis of fever of unknown origins will largely depend on the diagnosis of the underlying cause and will vary from patient to patient. If complications occur during a fever or unknown origins, this would be case dependent. However, patients with fever of unknown origins usually have a long term cause affecting them which is benign especially if there is absent substantial weight loss or any other abnormal symptoms that indicate a serious underlying condition such as cancer etc.
Hence, getting a professional’s advice on this issue is immensely important and plays a crucial role. The doctor is the only one who can give advice, diagnose, and get to the bottom of the underlying issue.