Osteomyelitis

There are an estimated 1.2 million intravenous drug abusers in the United States. (1) Most of the medical complications of IV drug abuse (IVDA) are caused by the actual administration of the drag rather than by the drug itself. Addicts rarely use aseptic techniques, and injection sites are often not cleaned fastidiously. This leads to a wide variety of clinical problems, ranging from mild cellulitis to more disseminated disease, such as osteomyelitis.

In the head and neck region, cellulitis and deep neck infections are the most common complications of IVDA. However, the concurrence of cervical vertebral osteomyelitis with a deep neck infection is often overlooked because of the insidious clinical presentation of the osteomyelitis. Delayed diagnosis and treatment of osteomyelitis may lead to more severe complications.

Case report

A 48-year-old man who was known to be an IV drug abuser presented to the emergency room with chief complaints of increased neck pain and dysphagia of 3 weeks' duration. He had been treated with oral antibiotics at another facility, but improvement was minimal. He was an active heroin user, and his most recent use had occurred within 24 hours of presentation. He denied injecting the drag into his neck.

On examination, the patient was awake and alert and had a low-grade fever. Findings on head and neck examination were significant for diffuse neck tenderness on palpation. No focal neurologic deficit was observed, and no abnormality was noted on fiberoptic laryngoscopy. His white blood cell count was 17,000/[mm.sup.3]. A lateral x-ray of the soft tissue of the neck identified retropharyngeal soft-tissue inflammation. Contrast-enhanced computed tomography (CT) of the neck demonstrated a large retropharyngeal abscess (figure 1).

[FIGURE 1 OMITTED]

The patient underwent incision and drainage of the retropharyngeal abscess via an intraoral approach under general anesthesia. Intravenous clindamycin was also started. Postoperatively, his symptoms did not improve, and he developed left upper-extremity weakness. Wound culture revealed methicillin-resistant Staphylococcus aureus that was sensitive to vancomycin, and therefore he was switched from clindamycin. We suspected osteomyelitis and paraspinal infection, but our initial evaluation on technetium ([sup.99]Tc) bone scanning of the spine detected no evidence of osteomyelitis. Further evaluation with magnetic resonance imaging (MRI) of the neck revealed multiple findings: a mild anterior epidural abscess in the spinal canal that extended from C2 to C4 with mild cord compression; a large degree of fluid collection with enhancement in the prevertebral soft tissue that extended from C1 to C6, which was consistent with a prevertebral abscess measuring 3.4 x 2.2 x 9.0 cm; and osteomyelitis involving the entire vertebral body of both C3 and C4 (figure 2). A neurosurgery consult was obtained. The neurosurgeons did not wish to operate. Therefore, the otolaryngology department performed the incision and drainage.

[FIGURE 2 OMITTED]

The patient underwent incision and drainage of the pre-vertebral abscess via a lateral neck approach on hospital day 8, and his symptoms subsequently resolved. He went on to complete 2 weeks of IV gentamicin therapy and 6 weeks of IV vancomycin.

Disease characteristics

Cervical vertebral osteomyelitis is an uncommon complication of IVDA, accounting for 2 to 4% of all skeletal infections secondary to IVDA. (2) Sapico and Montgomerie reviewed 67 cases of vertebral osteomyelitis in IV drug abusers and found that it was almost exclusively seen in male heroin users. (3)

Hematogenous spread is the most common route of entry, but it can also be caused by direct inoculation trauma, surgery, and contiguous spread of adjacent tissue infection. The most common pathogen in IVDA is Pseudomonas aeruginosa. The clinical course is usually insidious, and patients frequently do not seek medical care until 2 or 3 months following the onset of symptoms. Fever is the most common presenting symptom (42% of cases); only 15% of patients have transient neurologic deficits. (3) Laboratory findings in patients with osteomyelitis are nonspecific. Sapico and Montgomerie reported that 91% of patients had an elevated erythrocyte sedimentation rate and 35% had leukocytosis. (3) Our patient had a relatively short duration of symptoms and a low-grade fever, most likely because he had been previously treated with oral antibiotics. The presence of vertebral osteomyelitis was overlooked on initial presentation because of the obvious deep neck abscess.

Imaging

The diagnosis of vertebral osteomyelitis is nearly always dependent on radiologic study.

MRI. Mill has a sensitivity of 96% and a specificity of 92% in diagnosing vertebral osteomyelitis. (4) It has become the gold standard in the evaluation of osteomyelitis of the spine. (5) Other abnormalities related to osteomyclitis--such as epidural abscess, cord compression, and cord abscess-can also be identified on MRI. Classic findings include a decrease in the signal intensity of the affected disk and vertebral bodies on T1-weighted imaging and an increase in the signal on T2-weighted imaging. The involved disk and bone enhance after gadolinium administration. MRI was the definitive imaging modality in our patient.

CT. High-resolution CT, which cannot be used as a screening tool, is another excellent means of diagnosing osteomyelitis. Endplate erosions are usually more obvious and detected earlier on CT than on plain x-rays. The amount of epidural and paravertebral infection is also more easily noted on CT. It may be quite difficult at times to differentiate between neoplastic and infectious destruction of a vertebra on CT, but we know that tumors that are primarily lesions of bone generally spare disks, whereas infections destroy disks.

Bone scanning. The importance of radionuclide bone imaging studies has diminished since MRI became widely available. (5) A specific anatomic diagnosis can be made by MRI, but not by most nuclear scans. The sensitivity of [sup.99m]Tc bone scintigraphy for vertebral osteomyelitis is greater than 90%, but its specificity is lower than that of plain x-rays because most bone abnormalities are associated with a positive uptake of isotope. (6) An additional drawback to bone scanning is that its findings may be negative during the first week of infection. The bone scan failed to detect the osteomyelitis and related paraspinal infection in our patient--a further indication that it should not be considered as the first modality for the diagnosis of osteomyelitis.

X-ray. In the early stage of infection, findings on routine x-rays of the spine are often normal. The earliest findings include erosive changes in the vertebral endplates and narrowing of disk spaces, but they may not manifest until 2 to 8 weeks after the onset of infection.

Treatment

The mainstay of treatment for osteomyelitis is long-term IV antibiotics. Sapico and Montgomerie reported that 92% of patients responded to parenteral antibiotic therapy administered for 4 weeks or longer. (3) They reported no deaths or permanent neurologic sequelae. Surgery is indicated for patients who have a deep neck abscess or paraspinal abscess formation with obvious cord compression.

In conclusion, when a deep neck abscess in an IV drug abuser has failed to respond to treatment, the clinician should suspect vertebral osteomyelitis. We suggest that MRI be the first choice of imaging study in the evaluation of vertebral osteomyelitis and its complications.

References

(1.) Hahn RA, Onorato IM, Jones TS, Dougherty J. Prevalence of HIV infection among intravenous drug users in the United States. JAMA 1989;261:2677-84.

(2.) Dagirmanjian A, Schils J, McHenry MC. MR imaging of spinal infections. Magn Reson Imaging Clin N Am 1999;7:525-38.

(3.) Sapico FL, Montgomerie JZ. Vertebral osteomyclitis in intravenous drug abusers: Report of three cases and review of the literature. Rev Infect Dis 1980;2:196-206.

(4.) Modie MT, Masaryk TJ, Ross JS. Magnetic Resonance Imaging of the Spine. 2nd ed. St. Louis: Mosby, 1994.

(5.) Rothman SL. The diagnosis of infections of the spine by modern imaging techniques. Orthop Clin North Am 1996;27:15-31.

(6.) Alcantara AL, Tucker RB, McCarroll KA. Radiologic study of injection drug use complications. Infect Dis Clin North Am 2002;16: 713-43, ix-x.

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