A comparative evaluation of MRI, radionucleide bone scan and plain radiographs in Indian patients with spondyloarthropathy

Abstract

Background Spondyloarthropaties (SpA) are a diverse group of disorders characterized by inflammatory low backache, genetic predisposition and a variety of articular and extraarticular manifestations. Evidence of sacroiliitis in plain radiographs forms the cornerstone for establishing the diagnosis. However, it may take many years for the sacroiliitis to become visible. With the availability of biologics that have the potential to modify the course of SpAs, there is a need for early diagnosis of these disorders. Magnetic resonance imaging (MRI) and nuclear scintigraphy (radionuclide bone scan) appear promising in this context with their ability to pick up structural damage and inflammation before their presence is detected in plain radiographs. Objectives To assess the role of MRI and bone scan in patients with early SpA. Methods This was a cross sectional study done at a tertiary care rheumatology center of the armed forces. Patients satisfying the European Spondyloarthropathy Study Group (ESSG) criteria for Spodyloarthropathy and disease duration of less than 8 years were included. All patients underwent conventional radiography, MRI imaging and nuclear scintigraphy of the sacroiliac (SI) joints. The primary outcome assessed was the positivity rate for sacroiliitis of each of the three modalities in this group of patients. The sensitivity of each modality in contributing to the diagnosis over and above that of plain radiographs was assessed. Results Forty-four patients (predominantly young men, n = 39) with a median disease duration of 5 years were included in the study. Most patients had ankylosing spondylitis ( n = 21, 47.7%) closely followed by undifferentiated spondyloarthropathy ( n = 14, 31.8%), reactive arthritis ( n = 5, 11.1%) and psoriatic arthropathy ( n = 4, 9.2%). Evidence of sacroiliitis was seen in 59% (26/44) patients in plain radiographs, in 73% (34/44) with bone Scan and in 77% (34/44) with MRI. There was significant discordance among the three imaging modalities, documented in 49 of the 132 observations (37%). Amongst patients with a disease duration < 2 years (17/44, 39%), the plain radiographs showed changes in less than half the patients (8/17, 47%) with the MRI scan being positive in 88% of patients and the bone scan being positive in over 80% of patients. Though MRI and bone scan continued to have a higher pickup rate with increasing disease duration, the difference was most striking at 2 years. Amongst patients with undifferentiated spondyloarthropathies (USpA), ( n = 14), none of the patients had evidence of sacroiliitis on plain radiographs. However 10 (71.5%) patients each had evidence of sacroiliitis on MRI and bone scan, with 8 (57.1%) patients having both MRI and bone scan findings suggestive of sacroiliitis. Plain radiographs, MRI and bone scan, when used in combination, are able to detect sacroiliitis in almost all patients with SpA. Conclusions MRI had the maximum sensitivity (78%) for detecting sacroiliitis closely followed by bone scan (73%). Their utility was most apparent in patients with disease duration lesser than 2 years where plain radiographs have the least sensitivity in detecting sacroiliitis. They were also very useful in the subgroup of patients with uSpA where the radiographs were universally negative. MRI and bone scan individually picked up evidence of sacroiliitis in most of the patients with USpA and in combination picked up all the cases suggesting their usefulness in this group. However, there was a significant discordance rate amongst the three modalities and bone scan seems to lack specificity. MRI may be the preferred modality in patients with USpA and in those with early disease, given the poor specificity of bone scan.