Three patients with both ankylosing spondylitis and primary hyperparathyroidism were seen during a three-year period. The occurrence of these two relatively uncommon diseases in each patient raises the question of a possible, but unexplained, relationship between them.
Bunch TW, Hunder GG. Ankylosing Spondylitis and Primary Hyperparathyroidism. JAMA. 1973;225(9):1108–1109. doi:10.1001/jama.1973.03220370046012