Unexplained Fever: Causes and Solutions - Internal Medicine

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Fever of unknown origin (FUO)


I have been experiencing unexplained fevers every afternoon for the past six months, from November 1998 to May 1999.
Despite undergoing various tests, no cause has been identified, and I have not had any relief from the fever during this time.
I would like a physician's assistance in addressing this issue.

Zi Xuan, 10~19 year old female. Ask Date: 2010/05/11

Dr. Guo Hanyue reply Internal Medicine


Hello: There are many possible causes for fever of unknown origin, and if it lasts for six months, it is generally unlikely to be due to a bacterial or viral infection.
It is advisable to consult a dedicated infectious disease specialist to discuss the situation and evaluate the possibility of underlying issues such as immune disorders, chronic infections, tumors, or endocrine problems.
Additionally, if there is a long-term fever of unknown origin without significant weight loss or severe discomfort, and after thorough examinations no cause is found, the likelihood of a serious illness is relatively low.
(In the United States, about 30% of cases of fever of unknown origin remain unexplained.)

Reply Date: 2010/05/11

More Info


Unexplained fever, particularly when it persists for an extended period, can be a challenging medical issue. It is essential to understand that fever is not a disease itself but a symptom of an underlying condition. The causes of unexplained fever can be numerous and varied, ranging from infections to autoimmune diseases, malignancies, and even certain medications.
In your case, having experienced persistent fever for six months without a clear diagnosis is concerning and warrants a thorough investigation. The first step in understanding your condition is to consider the potential causes of your fever. Common categories include:
1. Infectious Diseases: These can include chronic infections such as tuberculosis, endocarditis (infection of the heart valves), or even viral infections that may not be easily detectable through standard tests. Sometimes, atypical pathogens or infections in unusual locations can lead to prolonged fever.

2. Autoimmune Disorders: Conditions like systemic lupus erythematosus (SLE), rheumatoid arthritis, or vasculitis can present with fever as a prominent symptom. These diseases often require specific blood tests and imaging studies to diagnose.

3. Malignancies: Certain cancers, particularly lymphomas or leukemias, can cause prolonged fevers. A thorough evaluation, including imaging studies and possibly a biopsy, may be necessary to rule out malignancy.

4. Medications: Some medications can induce fever as a side effect or due to an allergic reaction. A detailed medication history can help identify if this is a potential cause.

5. Other Causes: Conditions such as hyperthyroidism, deep vein thrombosis, or even certain metabolic disorders can lead to unexplained fever.

Given that you have undergone various tests without a definitive diagnosis, it may be beneficial to revisit your healthcare provider for a comprehensive evaluation. This may include:
- Detailed History and Physical Examination: A thorough review of your medical history, including any recent travel, exposure to sick individuals, or changes in your health, is crucial. A physical examination can help identify any signs that may have been overlooked.

- Laboratory Tests: Blood tests, including complete blood count (CBC), inflammatory markers (like ESR or CRP), and specific serologies for infections or autoimmune diseases, can provide valuable information.
- Imaging Studies: Depending on your symptoms and physical findings, imaging studies such as chest X-rays, CT scans, or ultrasounds may be warranted to look for hidden infections or tumors.

- Referral to Specialists: If initial evaluations do not yield answers, referral to specialists such as infectious disease experts, rheumatologists, or oncologists may be necessary for further investigation.

In conclusion, while unexplained fever can be frustrating and concerning, a systematic approach to diagnosis is essential. It is crucial to maintain open communication with your healthcare provider and advocate for further testing if your symptoms persist. Remember that persistent fever is a signal from your body that something is not right, and it deserves thorough investigation to identify and address the underlying cause.

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