A 28 year old former college athlete was admitted to the hospital with severe back pain.

Without apparent reason this previously healthy individual experienced the onset of lower back pain approximately three weeks prior to admission. He continued to work as a utility lineman for a couple of days after the onset of his pain but had to cease working as the pain became excruciating. Pain medicine as provided at the time of an urgent care visit proved insufficient. Chiropractic manipulation likewise did not provide significant relief.

Ultimately, he saw his primary care physician, and an MRI scan was ordered revealing evidence of discitis and vertebral osteomyelitis at L4-L5 (see top image at left). He underwent percutaneous aspiration of the L4-L5 disc. The radiologist who performed this procedure described aspiration of 10-15 cc of bloody-purulent fluid. A photomicrograph of a gram stain of microbial growth cultured by means of this procedure is shown at lower left.

During the course of the patient’s illness he may have had low grade fevers and mild night sweats. He did experience episodes of chills. He denied history of injectable drug use or the ingestion of unpasteurized dairy products. He had not engaged in recent international travel. His wife had had several episodes of carbuncular MRSA skin disease in the months prior to the onset of the patient’s illness.

At the time of the patient’s admission labs included WBC 10.5, Hgb 15.3 ESR 67 (H); LFT's were within normal limits. Two blood cultures were negative. He was begun on IV vancomycin and ceftazidime after his percutaneous biopsy.

This patient had discitis/vertebral osteomyelitis secondary to Haemophilus parainfluenzae.

Discitis/vertebral osteomyelitis (spondylodiskitis) is hema- togenous in origin in most cases and may be accompanied by adjacent infection of the epidural space and/or paraspinous muscles. Hematogenous infection of the vertebrae likely occurs via segmental arteries supplying the vertebrae and may arise from a variety of sources (skin and soft tissue, urinary tract, etc). The incidence of this disease appears to have increased in recent years though partly this could be an apparent increase related to improved means of diagnosis (MRI scanning).

Clinical symptoms of back pain related to spinal infection initially may be nonspecific and insidious though more acute presentations (similar to the one described here) may occur. A specific microbiologic diagnosis is required in order to choose optimal antimicrobial therapy. If blood cultures are not positive, then percutaneous aspiration of the infected disc/vertebral body often yields the infecting organism (in the absence of previous antibiotics). Specific antimicrobial therapy without surgery is often curative. Surgical intervention, however, may be necessary in cases of associated spinal epidural abscess with potential or actual neurological compromise.

Staphylococcus aureus is the most common cause of hema-
togenous discitis/vertebral osteomyelitis. However, in the case described the gram stain of the infecting organism revealed small gram negative cocco-bacillary forms. Of the choices offered in the preceding vignette, therefore, Brucella melitensis (Case of the Month #4) or Haemophilus parainfluenzae were the two most likely diagnoses. H parainfluenzae was identified by its growth on culture media and by specific biochemical tests. Worldwide Brucella species are by far a more common cause of osteo-articular disease than is Haemophilus parainfluenzae. In the United States, however, both of these organisms are exceeding rare causes of discitis/vertebral osteomyelitis. Pseudomonas aeruginosa is a cause of this disease particularly in intravenous drug users.

There are only a few published case reports of Haemophilus parainfluenzae as a cause of discitis/vertebral osteomyelitis. Unlike Haemophilus influenzae, H. parainfluenzae is a relatively uncommon cause of disease in humans. However, this bacterium is one of the HACEK organisms that can cause culture negative endocarditis. In the case described a trans-thoracic echocardiogram did not suggest the presence of infective endocarditis.

Ref: Zimmerli, W., Vertebral osteomyelitis, NEJM, 362;11, 1022-1029, 2010.