Diagnosis
Focal progressively severe back pain, fevers are rare; MRI is the best diagnostic test.
It is among the worst pain people can get.
Even if the patient has a pacer you can get an MRI if you do it right (PubMed).
Epidemiologic Risks
Seeding from bacteremia (especially in them what use needles), direct inoculation (especially from back surgery), and occasionally no good reason what so ever (although a history of preceding trauma is very common).
UTI, especially in men with obstruction, can get the urinary spread to the LS spine by way of Batson's plexus. Shazam (PubMed).
And if you have S. aureus in the blood and the bladder, worry re: LS spine discitis/epidural abscess.
Microbiology
Usually S. aureus, coagulase-negative staphylococcus, and oral streptococci.
P. acnes is seen post-op, Candida on occasion in the heroin user.
About 10% of spontaneous infections are due to coagulase-negative staphylococcus (PubMed) often a complication of a central line.
You cannot tell the difference between gram-positive or gram-negative infections (PubMed) except, of course, if you culture the disc space. So get a biopsy first.
De novo infected discs can have anaerobes, including P. acnes. If the MRI is the right type (disc herniation with Modic Type 1) the herniated disc may indeed be infected (PubMed) (Review)(PubMed), although not supported in all studies, as is so often the case (PubMed).
Empiric Therapy
Baaaaaaaad idea. Get a biopsy first. The microbiology and resistance patterns are unpredictable; it is too easy to guess wrong. No bug, no drug. But work with alacrity in areas of the spinal cord: not only can it progress to an epidural abscess but on occasion, the infection will cause a vertebral artery thrombosis and then cord infarction. So if the biopsy isn’t going to happen that day, start antibiotics, perhaps an anti-MRSA agent plus a third-generation cephalosporin.
And then there is the study where patients with Modic 1 changes on MRI were randomized to under dosed amoxicillin/clavulanic and got more better than placebo (PubMed). My advice, if you have a patient who presents with the MRI and history suggestive of infection, re-read the preceding paragraph.
Surgery leads to better outcomes: "In short, early surgical treatment of pyogenic spondylodiscitis typically achieves a better prognosis, shorter hospitalization period, and subsequent significant improvement in kyphotic deformity and quality of life" (PubMed). Now to make the surgeons a believer.
Specific Therapy
Once you get an organism it is 6 to 8 weeks of IV therapy directed against the infecting organism. If the patient is improving clinically (decreasing pain, ESR) there is no reason to repeat the MRI, it gives no useful information (PubMed).
"...early surgical treatment of pyogenic spondylodiscitis typically achieves a better prognosis, shorter hospitalization period, and subsequent significant improvement in kyphotic deformity and quality of life."(PubMed). Although for every study there is an equal and opposite study "No additional long-term beneficial effect of surgical treatment could be shown in the studies comparing surgical versus antibiotic only treatment." (PubMed). I still lean towards debridement, being a big fan of surgical source control.
Pearls
Infection ALWAYS goes to the disk then spreads to the contiguous bone, destroying endplates in the process; tumor ALWAYS goes to bone and spares the endplates and disk space. You can take that to the bank. To date, I have seen one exception.
Curious Cases
Relevant links to my Medscape blog
Last Update: 06/22/18.