N.B. Gaylis, S.D. Needell, D. Rudensky

CHANGES IN EROSIVE STATUS DETECTED ON IN-OFFICE MRI AFTER ONE YEAR FOLLOW-UP OF RHEUMATOID ARTHRITIS PATIENTS ON INFLIXIMAB THERAPY

Background: Magnetic resonance imaging (MRI) is more sensitive than conventional radiographs in detecting and monitoring changes in bone erosions in response to therapy. MRI can be beneficial in helping to determine the absolute benefit of therapy on patient’s response.

Objectives: To evaluate changes in baseline and follow-up erosive status in rheumatoid arthritis (RA) patients treated with infliximab utilizing an in-office MRI system and to determine if there are differences in outcome based on disease duration at baseline. To quantify the distribution of erosive changes in the hand and wrist.

Methods: Patients who satisfied the American College of Rheumatology criteria for RA and who were receiving infliximab therapy were evaluated with two MRI studies conducted at least 12 months apart. The studies were interpreted by a fellowship–trained musculoskeletal radiologist blinded to patient clinical presentation. The MRI System (Magnevu 1000, Carlsbad, California, Self-shield low-field [0.2 Tesla scanner]) operates on standard 110-volt power supply and occupies minimal office space. Bone erosions were identified as well-defined defects extending through the cortical margin. Signal characteristics for erosions were low signal intensity on T1 weighted images and high signal intensity on short tau inversion (STIR) images. Regression or healing of erosions was measured by a reduction in erosion size, accompanied by an increase in T1 signal intensity. In some cases, erosions showed a decrease in STIR signal intensity.

Results: Disease duration was <1 year in 13 patients, <2 years in 7 patients, 3 to 5 years in 9 patients, and >5 years in 19 patients. The median infliximab dosage was 4 mg/kg (range, 3 to 6 mg/kg) with an approximate infusion interval of 7 weeks.

At baseline, of the 83 MRIs conducted in 41 patients, 64 exams were positive for erosions (77%); 7 patients had no erosions; 45 of 83 exams (54%) were positive for MCP erosions in 34 patients; 36 of 83 (43%) carpal bone exams were positive for erosions in 24 patients; 1 erosion was detected from 2 MTP exams. Of 35 bilateral examinations, 13 patients had bilateral erosions and 6 patients had unilateral erosions. 25 patients with MCP erosions did not have carpal erosions while only 16 patients with carpal erosions had no MCP erosions. 13 had MCP erosions unilaterally. 12 had wrist erosions unilaterally. Follow-up MRI evaluation revealed regression of 9 MCP erosions, 8 carpal erosions, and 1 MTP erosion for a total of 18 in 11 patients. Thirty-four patients showed no change in disease. Four exams(3 MCP, 1 carpal)showed progression in size and/or number of erosions in 3 patients. The use of infliximab was associated with stability of erosions in 75% and regression of erosions in 20%. MRI evidence of erosion healing was detected with similar frequency in the metacarpal phalangeal joints and in the carpus.

Patients were further divided into patients recently diagnosed (≤5 years) and patients with long-standing disease. There were no significant differences in the frequency or accuracy of detection of erosions between the two groups.

Erosion status at baseline [A] and at 1-year of follow-up [B]

Erosion status

X-ray Positive

Negative

MRI Positive

Negative

[A] Baseline erosion status

Joints evaluated

MCP

19 (12)

34(19)

30 (23)

23 (8)

Carpus

16 (11)

37 (20)

26 (19)

27 (12)

[B] Erosion status at 1-year

Regardless of baseline status

No change

52 (30)

40(22)

Progression

–

1(1)

Regression

1(1)

12 (8)

Conclusion: In-office MRI was approximately twice as sensitive as x-ray in detecting erosions at baseline. This has implications with regards to the choice of therapy offered to RA patients. In contrast to standard radiographs, MRI was also useful to monitor disease response after the initiation of infliximab, in both early and long-standing RA. Utilization of infliximab was associated with inhibition of disease progression and preservation of joint integrity in RA.

Click here for a PDF version of the article published in the Japan Journal of Rheumatology.