Current issues of ACP Journal Club are published in Annals of Internal Medicine


Diagnosis

Magnetic resonance imaging for multiple sclerosis had high sensitivity and varying specificity

ACP J Club. 1993 Nov-Dec;119:76. doi:10.7326/ACPJC-1993-119-3-076


Source Citation

Offenbacher H, Fazekas F, Schmidt R, et al. Assessment of MRI criteria for a diagnosis of MS. Neurology. 1993 May,43:905-9.


Abstract

Objective

To compare the diagnostic value of 4 sets of magnetic resonance imaging (MRI) criteria for patients with suspected multiple sclerosis (MS).

Design

A comparison of blinded reading of MRI brain scans used to compile 4 criteria sets with a final diagnosis of MS based on clinical criteria.

Setting

A university hospital in Austria.

Patients

MRI brain scans from 1528 consecutive patients were read by 1 clinician blinded to final diagnosis. Patient age was 12 to 93 years and 786 patients were women. 134 patients were referred because of suspicion of MS (mean age 39 y, 89 women).

Description of tests and diagnostic standard

Brain MRI was done using a 1.5-tesla magnet and only transverse proton-density and T2-weighted spin-echo images were interpreted (presence, number, size, and location of areas of increased signal [AIS]). For the patients with suspected MS, the diagnosis was verified by chart review for 88 and by physician questionnaires for 46 (82 definite MS, 29 probable MS, 23 possible MS, using clinical criteria).

Main outcome measures

Sensitivity, specificity, and positive predictive value for ≥ 3 AIS, ≥ 4 AIS (Paty A criteria), ≥ 3 AIS and 1 of the AIS bordering the lateral ventricles (Paty B criteria), and ≥ 3 AIS plus 2 of AIS abutting the body of lateral ventricles, infratentorial lesion location, or size > 5 mm (Fazekas criteria).

Main results

AIS were present in 96% of patients in the MS group and in 40% of patients in the non-MS group. 3 or more AIS were present in 90% of patients in the MS group and in 29% of the non-MS group. The sensitivity, specificity, positive and negative likelihood ratios (+LR, -LR), and positive predictive value for definite, probable, and possible MS for ≥ 3 AIS were 90%, 71%, {3.10 and 0.14}*, and 23%; for Paty A criteria, 87%, 74%, {3.35, 0.18}*, and 25%; for Paty B criteria, 87%, 92%, {10.86, 0.14}*, and 50%; and for Fazekas criteria, 81%, 96%, {20.25, 0.20}*, and 65%, respectively. Both specificity and positive predictive values decreased with age. Multivariate analysis showed that AIS abutting the temporal horn, abutting the bodies of the lateral ventricles, abutting the 4th ventricle, and a lesion > 5 mm were the best predictors of MS.

Conclusion

Magnetic resonance imaging of the brain for the diagnosis of multiple sclerosis had high sensitivity and varying specificity and positive predictive values depending on the criteria used and the age of the patient.

Source of funding: Not stated

For article reprint: Dr. F. Fazekas, Department of Neurology, Karl-Franzens University, Auenbruggerplatz 22, A-8036 Graz, Austria.

*Numbers calculated from data in article.


Commentary

Magnetic resonance imaging was better than computed tomography for diagnosing multiple sclerosis

MS is a clinical diagnosis that is made best by a neurologist. Supportive tests include neuroimaging, evoked responses, urologic testing, and cerebrospinal fluid studies of IgG production and oligoclonal bands. These supportive tests help define research diagnostic criteria for clinical trials (1) and provide more diagnostic certainty for the patient. A potential diagnosis of MS causes great unease, prompting continued interest in confirming a diagnosis or ruling out MS as early as possible in patients with nonspecific neurologic symptoms.

AIS seen on MRI are found in MS and in a variety of other conditions including "healthy aging." The number, size, and location of AIS help differentiate MS from other neurologic diseases. The study by Offenbacher and colleagues adds important information on the sensitivity, specificity, and positive predictive value of several AIS diagnostic criteria. For an individual patient, the tables on positive predictive value and specificity will allow clinicians to assess just how supportive a given scan is of the clinical diagnosis of MS.

In a patient with 2 attacks of MS where clinical evidence of only 1 central nervous system lesion is present, MRI evidence of a separate lesion or positive test results for cerebrospinal fluid allow the diagnosis of definite MS to be made (1). These tests add to our knowledge about patients with monosymptomatic optic neuritis or acute myelopathy but do not allow definite diagnosis of MS to be made in such patients (1).

The study by Mushlin and colleagues confirms the utility of an MRI scan considered definite for MS (e.g., containing the multiple white matter and periventricular lesions). Unfortunately, only 36% of the patients with MS had such a characteristic MRI result. The low (1%) false-positive rate for such classic findings using MRI confirmed the diagnosis for approximately 20% of patients having an MS evaluation who were now spared the anguish of an equivocal diagnosis. Unfortunately, half of the patients sent for MRI in this study had a negative result (MRI report of "probably not" or "definitely not" MS), even though more than 25% of these patients were judged clinically to have MS. Thus, a negative MRI does not rule out MS. MRI scanning is the preferred imaging technique for MS. Mushlin and colleagues compared double-contrast CT imaging with MRI and found that MRI was markedly better. MRI is more likely to show abnormalities in a patient with MS than CT, evoked responses, or cerebrospinal fluid examinations (2). The false-negative rate of the combination of these studies is low but not sufficiently low to fully reassure the patient—watchful waiting is still necessary.

Progress in neuroimaging continues at a fast pace, and new techniques are being evaluated for patients with clinical syndromes prompting an MS evaluation (2). Additional studies will clarify the utility of paramagnetic contrast agents and alternative MRI techniques. Serial MRI scanning, with or without gadolinium-diethylenetriamine penta-acetic acid enhancement, has been used successfully to monitor treatment effects. Echo-planar MRI (allowing imaging after functional activation), magnetic resonance spectroscopy imaging (allowing quantitation of certain tissue components), positron emission tomography, and electroencephalographic imaging are all procedures that may improve our future diagnostic certainty for early or atypical MS, as will our abilities to provide patients with prognostic information and to better monitor their treatment.

Jay S. Luxenberg, MD
The Mount Zion Institute on AgingSan Francisco, California, USA


References

1. Poster CM, Pay DW, Scheinberg L, etal. New diagnostic criteria for multiple sclerosis: guidelines for research protocols. Ann Neurol. 1983;13:227-31.

2. Goodkin DE, Rudick RA, Ross JS. The use of brain magnetic resonance imaging in multiple sclerosis. Arch Neurol. 1994;51:505-16.