Correspondence

Magnetic Resonance Imaging

N Engl J Med 1993; 329:434-435August 5, 1993

Article

To the Editor:

Edelman and Warach provide a comprehensive review of magnetic resonance imaging (MRI) (March 11 and 18 issues)1. They compare MRI with bone scintigraphy and note that MRI is “the imaging method of choice for acute osteomyelitis.” There have been a number of studies comparing various imaging techniques for diagnosing osteomyelitis in diverse patient populations. We have found leukocyte scanning with oxyquinoline labeled with indium-111 to have greater sensitivity and accuracy than MRI in diagnosing osteomyelitis in diabetic foot ulcers, using bone biopsy for culture and histologic examination as the gold standard in all cases2.

We speculate that the greater sensitivity of leukocyte scanning as compared with MRI may be due to the presence of inflammatory cell infiltration in bone detectable by leukocyte scanning before the structural bone changes discerned by MRI appear during the course of osteomyelitis. The limitations of MRI in diagnosing osteomyelitis also include false positive results in patients with fracture, infarction, healed infection, or postoperative procedures3,4. In addition to improved accuracy, leukocyte scanning compares favorably with MRI in terms of cost, because it is approximately 30 percent less expensive.

Lisa G. Newman, M.D.
Mount Sinai Medical Center, New York, NY 10029

4 References

1. 1

   Edelman RR, Warach S. Magnetic resonance imaging. N Engl J Med 1993;328:708-16, 785
   Full Text | Web of Science | Medline

2. 2

   Newman LG, Waller J, Palestro CJ, et al. Leukocyte scanning with 111 In is superior to magnetic resonance imaging in diagnosis of clinically unsuspected osteomyelitis in diabetic foot ulcers. Diabetes Care 1992;15:1527-1530
   CrossRef | Web of Science | Medline

3. 3

   Berquist TH, Brown ML, Fitzgerald RH Jr, May GR. Magnetic resonance imaging: application in musculoskeletal infection. Magn Reson Imaging 1985;3:219-230
   CrossRef | Medline

4. 4

   Erdman WA, Tamburro F, Jayson HT, Weatherall PT, Ferry KB, Peshock RM. Osteomyelitis: characteristics and pitfalls of diagnosis with MR imaging. Radiology 1991;180:533-539
   Web of Science | Medline

To the Editor:

Edelman and Warach state that the use of myelography in the diagnosis of spinal disorders has been “virtually eliminated” by the use of MRI. This statement is misleading, particularly as it applies to nerve-root syndromes. Edelman and Warach cite two early articles1,2 whose authors, however, acknowledge a clear additional advantage in diagnostic accuracy if computed tomography (CT) is added to MRI.

Spine surgeons often use MRI as a screening tool for radicular syndromes. If the diagnosis is clear-cut, no further studies are undertaken. If the diagnosis is in doubt or if the anatomical features need clarification before surgery, CT enhanced by myelography is the supplemental study of choice. This technique best demonstrates actual nerve-root compression or displacement, which is the single most important radiographic criterion for surgical treatment. . . . Contrast CT offers the best choice when the clear presence of root compression is not confirmed by MRI.

Ronald Birkenfeld, M.D.
2110 Dorchester Ave., Boston, MA 02124

2 References

1. 1

   Modic MT, Masaryk T, Boumphrey F, Goormastic M, Bell G. Lumbar herniated disk disease and canal stenosis: prospective evaluation by surface coil MR, CT, and myelography. AJR Am J Roentgenol 1986;147:757-765
   Web of Science | Medline

2. 2

   Modic MT, Masaryk TJ, Mulopulos GP, Bundschuh C, Hans JS, Bohlman H. Cervical radiculopathy: prospective evaluation with surface coil MR imaging, CT with metrizamide, and metrizamide myelography. Radiology 1986;161:753-759
   Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: We agree completely with the premise expressed in these letters that optimal patient care must be based on the specifics of the clinical presentation and the knowledge and experience of the physician rather than on blind adherence to a diagnostic algorithm.

Dr. Newman cites her own study suggesting that indium-111-labeled leukocyte scanning is more sensitive than MRI for the diagnosis of osteomyelitis associated with diabetic foot ulcers. Her study prospectively examined only 16 lesions. Another prospective study of 16 lesions, also using bone biopsy as the gold standard, found excellent sensitivity for both MRI and indium-111-labeled leukocyte scanning in the diagnosis of osteomyelitis,1 whereas a third study of 23 patients found MRI to be the more sensitive technique (72 percent vs. 45 percent)2. The study of Erdman et al. to which Dr. Newman refers was based on 110 patients and found an overall sensitivity of 98 percent for MRI in the diagnosis of osteomyelitis. Until a large prospective study comparing MRI and indium-111-labeled leukocyte scanning is undertaken, we must reserve judgment about their relative sensitivity and specificity in the diagnosis of osteomyelitis.

Dr. Birkenfeld is correct in pointing out that if the results of spinal MRI are ambiguous, the combination of CT and myelography may provide additional information. His belief that contrast CT is superior to MRI in the detection of nerve-root compression is at odds with recent prospective comparisons, which have found that the accuracy of MRI does not differ from that of CT plus myelography in the diagnosis of cervical3 or lumbar4 radiculopathy. MRI has fewer risks and is usually preferred. Some spine surgeons, however, may prefer to get their diagnostic information from the test that is more familiar to them. Newer MRI techniques, although not yet compared with CT plus myelography, show even more detail of nerve roots and can display them in three dimensions5. We stand by the accuracy of our statement that in many institutions, including our own, myelography has been virtually replaced by MRI.

We question whether a clinical diagnosis that is not in doubt always requires confirmation by a test. We caution against excessive reliance on MRI or any test for clinical decision making, when it is the patient we must treat and not the test result.

Steven Warach, M.D., Ph.D.
Robert R. Edelman, M.D.
Beth Israel Hospital, Boston, MA 02215

5 References

1. 1

   Seabold JE, Flickinger FW, Kao SC, et al. Indium-111-leukocyte/technetium-99m-MDP bone and magnetic resonance imaging: difficulty of diagnosing osteomyelitis in patients with neuropathic osteoarthropathy. J Nucl Med 1990;31:549-556
   Web of Science | Medline

2. 2

   Williamson MR, Quenzer RW, Rosenberg RD, et al. Osteomyelitis: sensitivity of 0.064 T MRI, three-phase bone scanning and indium scanning with biopsy proof. Magn Reson Imaging 1991;9:945-948
   CrossRef | Web of Science | Medline

3. 3

   Brown BM, Schwartz RH, Frank E, Blank NK. Preoperative evaluation of cervical radiculopathy and myelopathy by surface-coil MR imaging. AJR Am J Roentgenol 1988;151:1205-1212
   Web of Science | Medline

4. 4

   Thornbury JR, Fryback DG, Turski PA, et al. Disk-caused nerve compression in patients with acute low-back pain: diagnosis with MR, CT myelography, and plain CT. Radiology 1993;186:731-738
   Web of Science | Medline

5. 5

   Krudy AG. MR myelography using heavily T2-weighted fast spin-echo pulse sequences with fat presaturation. AJR Am J Roentgenol 1992;159:1315-1320
   Web of Science | Medline