Correspondence to: C. C. Mok. E-mail: ccmok2005{at}yahoo.com
A 44-yr-old Chinese woman enjoying good health presented with progressive low back pain for 8 yr. Physical examination revealed tenderness at the lumbar spinal processes but not at the sacroiliac joints. Movements of the lumbar spine were limited in all planes. There were no skin lesions, peripheral arthritis or enthesitis. Rheumatoid factor and HLA-B27 were negative.
Plain X-rays of her lumbar and thoracic spine demonstrated undulating calcifications of the anterior longitudinal ligaments involving at least four consecutive vertebral bodies. Intervertebral disc height was relatively preserved. Ectopic calcifications of the iliolumbar ligaments and hip joints were also present. An MRI did not show features of sacroiliitis.
Incidentally, she was found to have hypocalcaemia (adjusted serum calcium level 1.45 mmol/l; normal range 2.102.55 mmol/l) and hyperphosphataemia (1.81 mmol/l; normal range 0.911.55 mmol/l). The serum parathyroid hormone (PTH) level was grossly elevated (18.3 pmol/l; normal range 1.66.9 pmol/l). A CAT scan of the brain revealed calcification of the basal ganglia.
Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by hyperostosing and ossifying enthesopathies involving the spine and extra-axial structures [1]. DISH usually affects older individuals and common presenting features are spinal rigidity and polyenthesopathies, simulating the inflammatory spondyloarthropathies. In our patient, the radiological differential diagnoses include DISH, ankylosing spondylitis (AS) and degenerative spondylosis. The absence of true syndesmophytes, apophyseal joint ankylosis, sacroiliitis and a negative HLA-B27 virtually excludes AS. The relatively young age and the absence of degenerative changes in the intervertebral discs make lumbar spondylosis unlikely.
Pseudohypoparathyroidism (PHP) is a hereditary disorder characterized by a defective end-organ response to PTH. Chronic hyperphosphataemia may induce ectopic calcifications of the skeletal and soft tissues, mimicking the radiological appearance of DISH. However, these calcifications are often incidental. The long history of back pain in our patient raises the possibility of the co-existence of DISH and PHP, which has hitherto been unreported.
The authors have declared no conflicts of interest.
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