AS, DISH or something else?

A 68-year-old farmer presented with progressively worsening pain in multiple joints associated with stiffening for 9 months. Locomotor examination revealed grossly restricted movement of the axial skeleton. There were no neurological deficits. Radiological evaluation demonstrated diffuse bone densification and extraspinal calcification with bony ankylosis reminiscent of ankylosing spondylitis. Laboratory tests subsequently yielded the true diagnosis. The patient was counselled accordingly and started on appropriate therapy.