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Fever of Unknown Origin

“Over the last few weeks I just keep getting these night sweats.  I’m all achy and tired… I just don’t feel good.  I’ve checked my temperature and it’s gone over 101 degrees several times in the last few weeks.”  Mrs. Brown looked moderately ill, but after a physical exam the only abnormalities were her usual heart murmur, maybe a little louder than usual, and some mild tenderness around her low back.  Blood work came back mostly normal except for a slightly high level in her sedimentation rate (sed rate – a general marker for inflammation or infection in the body), and a borderline high white blood count (WBC), also usually an indicator of infection.

So, we were left with rather general symptoms, an unremarkable physical exam, and a couple of general abnormal lab findings, but no specific source for the infection.  Though it’s not always ideal, sometimes an initial course of a broad spectrum antibiotic is given to see if this clears the fever and other symptoms or whether a further work-up will be needed.  This was done with Mrs. Brown and she came back stating she felt much better and that the fever and night sweats had cleared.  Likewise her WBC and sed rate were nearly normal.  We told her to get back to us if the symptoms returned once she was off the antibiotic, and sure enough, they did.

Mrs. Brown generally fell into a category called fever of unknown origin (FUO).  Basically, FUO’s are described as a recurrent fever of 101 or greater over a course of 3 or more weeks with no obvious source despite an adequate workup to find one.  FUOs may be caused by infections (30-40%), tumors (20-30%), rheumatologic diseases like rheumatoid arthritis or lupus (10-20%), and numerous miscellaneous diseases (15-20%).  In studies, between 5 and 15% of FUO cases remain undiagnosed despite extensive studies.

Some of the specific causes of FUO’s include heart valve infections, tuberculosis, lupus, urinary tract infections, abscesses (sometimes on internal organs), bone infections, HIV, fungal infections, parasites, long-acting viruses, lymphoma, leukemia, solid tumors, fevers caused by medications, and a long list of even more uncommon causes.

When, as in Mrs. Brown’s case, the symptoms are rather general and vague, the workup can be difficult and the answer elusive.  Over time, Mrs. Brown complained more about her low back being particularly painful as her fever kept recurring and her sed rate continued to climb.  An x-ray and then an MRI of the lumbar (lower) spine showed an uncommon infection of a disc between two vertebrae, an infection called, discitis.  Likewise one of a few blood cultures that were drawn grew out a type of Strep bacteria.  Sometimes this type of bacteria first infects a heart valve, having gotten there through the blood stream from the mouth, perhaps after some dental work.  If so, the bacteria will damage the heart valve as well as traveling from there to other places in the body, like a disc in the spine.

At any rate, Mrs. Brown ended up needing intravenous antibiotics to clear this serious infection, and may need back surgery as well.  The bottom line is that some FUO’s turn out to be relatively minor viral infections while others are markers for much more serious illnesses.  Hopefully you’ll never experience weeks of unexplained fever, but if you do, best to get it investigated sooner rather than later.

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