Presence of spondyloarthropathy and its clinical profile in patients with hypoparathyroidism

Abstract

Background: Though spondyloarthropathy has been described in patients with sporadic idiopathic hypoparathyroidism (SIH), the clinical profile is not known. Objectives: To describe the clinical profile including radiological features of spondyloarthropathy and prevalence of HLA-B27 allele in patients with hypoparathyroidism, and to identify any differences from ankylosing spondylitis. Subjects and methods: Clinical characteristics and radiographs of pelvis and spine were assessed in 40 consecutive patients with SIH. Radiographs were assessed by radiologist (RS) and rheumatologist (RG) for the features of spondyloarthropathy including sacroiliitis, syndesmophytes and hip joint calcification, and so on. HLA-B27 genotyping was carried out in patients with SIH, and 195 healthy controls using duplex PCR. Fourteen control radiographs were from age-matched normal individuals. Results: Three patients with SIH had clinically overt spondyloarthropathy which closely resembled ankylosing spondylitis. Fourteen (eight females and six males) of the 40 patients with SIH showed radiological changes including syndesmophytes in lower dorsal or dorso-lumbar spine (n = 6), sacroiliitis and new bone formation at the acetabular rim of the hip joint (n = 10). Though all six patients demonstrating syndesmophytes had new bone formation at hip, sacroiliitis was seen in only three of them. None of the 14 controls had syndesmophytes, sacroiliitis or hip joint calcification. The mean (SD) duration of illness (15.4 ± 8.7 vs. 6.5 ± 5.9 years, P < 0.01), BMI (24.1 ± 5.2 vs. 20.8 ± 3.7 kg/m², P = 0.04) and frequency of basal ganglia calcification was higher (100%vs. 57.7%, P < 0.01) in patients who showed changes of spondyloarthropathy in comparison to those without these changes. On multiple logistic regression analysis, only duration of hypoparathyroid illness was associated with spondyloarthropathy with an odds ratio of 1.17 (95% CI = 1.05-1.30, P < 0.01) per year increase in the duration. The mean age, serum total calcium, inorganic phosphorus and serum intact PTH (iPTH) levels were not significantly different between SIH patients with and without spondyloarthropathy. The frequency of HLA-B27 allele was comparable between SIH and the control groups. Conclusions: Thus, spondyloarthropathy is a distinct clinical entity in patients with SIH. Its salient clinical features include presence of syndesmophytes at the thoracic or thoraco-lumbar spine, mild sacroiliitis, calcification at the acetabular margin of hip, preserved bone density, equal distribution in both sexes and lack of HLA-B27 association. Presence of spondyloarthropathy, like basal ganglia calcification, is associated with longer duration of hypoparathyroidism. It is important to differentiate hypoparathyroid-related spondyloarthropathy from ankylosing spondylitis because the management for the two disorders is different.