PHILADELPHIA — Using MRI to help classify spondyloarthritis poses a significant risk for error, according to findings from a multicenter study that evaluated 85 MRI scans.

A panel of five rheumatologists and radiologists specially trained in MRI assessment of lesions associated with spondyloarthritis (SpA) in the sacroiliac joint misclassified 6 of 85 cases based on their MRI scans, Dr. Ulrich Weber said at the annual meeting of the American College of Rheumatology.

The finding underscores the importance of establishing reliable thresholds for diagnosing significant SpA-associated pathology in MRI scans of sacroiliac joints, said Dr. Weber, a rheumatologist at the Balgrist University Clinic in Zurich, Switzerland. “MRI will never be 100% accurate for confirming a diagnosis of SpA. Low-grade active and chronic abnormalities [on MRI] are seen in up to a third of healthy volunteers and patients with non-specific back pain.”

The findings, “underscore the limitations of reading MRI, even in the hands of trained readers,” commented Dr. John D. Reveille, professor of internal medicine and director of the division of rheumatology and clinical immunogenetics at the University of Texas Medical School at Houston.

Although sacroiliitis identified by plain radiography has been the traditional method for classifying SpA, MRI has been increasingly used. MRI's role for classifying SpA solidified in 2009 with the publication of the SpA classification criteria of the Assessment of Spondyloarthritis International Society (ASAS) (Ann Rheum Dis. 2009;68:777-83). In this paper, ASAS said that MRI scans showing “active (acute) inflammation of sacroiliac joints … highly suggestive of sacroiliitis associated with SpA” could substitute for radiographic evidence when classifying a patient as having SpA.

To examine the consequences of MRI assessment, Dr. Weber and his associates developed a training program to teach rheumatologists and radiologists to identify sacroiliac joint pathology indicative of SpA. The classification criteria focused on four features of active inflammation: bone marrow edema, erosion, fatty infiltration, and ankylosis. They then had a panel of two radiologists and three rheumatologists who underwent training review MRI scans from 59 asymptomatic healthy volunteers and 26 patients with nonspecific back pain of mechanical origin. All subjects were age 45 years or younger.

Among the 59 healthy volunteers, one or more of the panel members misclassified four (7%) as having MRI features indicative of SpA. When reviewing the 26 patients with mechanically induced lower back pain, panel members misclassified two (8%) as having SpA.

The error rate was even higher for some of the individual assessment elements. At least two panel members identified some degree of bone marrow edema in 22% of the healthy volunteers and in 38% of the patients with nonspecific, mechanical back pain.

Two panel members scored the bone marrow edema clinically relevant in 12% of the healthy volunteers and in 23% of the patients with mechanically triggered back pain.

Roughly similar mistake rates occurred when the panelists scored the MRIs for bone erosions and for fatty infiltrations.

The physicians who read MRI scans of back pain patients need careful training and clear guidance on what constitutes SpA lesions in sacroiliac joints, accordng to Dr. Weber.

Disclosures: Dr. Weber said that he and his associates had no financial disclosures relevant to his presentation on SpA and MRI.

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'MRI will never be 100% accurate for confirming a diagnosis of SpA.'

Source DR. WEBER

My Take

Knowing How to Use MRI Is Key

I would agree that the isolated use of an MRI evaluation of the sacroiliac joint would be subject to false-positive error for the diagnosis of ankylosing spondylitis. The value of the MRI findings needs to be used in combination with the other features that are seen with AS, which is why the diagnosis is based upon multiple criteria. Nevertheless, in conjunction with other findings the ability to recognize inflammation of the sacroiliac joint in particular with negative radiographs has been well reported to improve the diagnostic yield significantly.

I would agree that an experienced radiologist needs to interpret the significance of the MRI findings as is evidenced by Dr. Ulrich Weber's findings. The false positives reported may well have been avoided in experienced radiologist's hands. In fact, sensitivity of MRI is always an issue. That does not mean it is a bad tool. Like driving a race car, you have to know how to handle and interpret the high tech equipment you are utilizing.

NORMAN B. GAYLIS, M.D., president of the International Society of Extremity MRI in Rheumatology, is in private practice in Aventura, Fla. He has written and lectured widely on in-office use of imaging in rheumatology. Dr. Gaylis reports financial relationships with numerous pharmaceutical companies.

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DR. GAYLI

Misclassifying Spondyloarthritis: MRI Held Risky