Poster Presentation 29th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2019

Atypical fracture in an atypical location after intermittent bisphosphonate use unmasks a diagnosis of hypophosphatasia – a novel case report (#157)

Jack Lockett 1 2 , Usman H Malabu 1 3 4 , Emma Lyster 5 , John Maguire 4 , Yong Mong Tan 1 3 4
  1. Department of Diabetes and Endocrinology, The Townsville Hospital, Douglas, QLD, Australia
  2. Faculty of Medicine, The University of Queensland, Brisbane, QLD, Australia
  3. College of Medicine and Dentistry, James Cook University, Douglas, QLD, Australia
  4. Mater Hospital, Pimlico, QLD, Australia
  5. Townsville Family Medical Centre, Currajong, QLD, Australia

Atypical femoral fractures are associated with long term bisphosphonate (BP) use.1 Fractures at other sites have been described following BP use.1 Atypical femoral, but not tibial, fractures have also been reported with adult hypophosphatasia (HPP).2,3 Here we report the unusual case of an atypical proximal tibial fracture (APTF) after intermittent use of BP leading to a new diagnosis of adult hypophosphatasia. We describe a 63-year old Caucasian woman who suffered APTF after 5 years of intermittent exposure to alendronate given for recurrent metatarsal stress fractures. Bisphosphonate administration was stopped following the APTF. Review of her previous serum ALP levels revealed consistently low levels. Adult hypophosphatasia was diagnosed from the low serum ALP activity and elevated urine phosphoethanolamine levels.2  She was managed conservatively on analgesics. Adult HPP is an under-recognised condition associated with atypical insufficiency fractures due to inorganic pyrophosphate-mediated inhibition of bone mineralisation.2,4 Bisphosphonate use compounds this hazard due to inhibition of bone turnover and remodelling in already at-risk bones.2 Our report is the first case of intermittent BP exposure preceding APTF in adult HPP and highlights the uncommon site of the proximal tibia for BP associated atypical insufficiency fractures, the need to screen for HPP in those with persistently low ALP prior to commencement of BP, and the importance of avoiding BPs in HPP.

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  2. Sutton RA, Mumm S, Coburn SP, Ericson KL, Whyte MP. "Atypical femoral fractures" during bisphosphonate exposure in adult hypophosphatasia. J Bone Miner Res. 2012;27(5):987-994.
  3. Bhattacharyya T, Jha S, Wang H, Kastner DL, Remmers EF. Hypophosphatasia and the risk of atypical femur fractures: a case-control study. BMC Musculoskelet Disord. 2016;17:332.
  4. Berkseth KE, Tebben PJ, Drake MT, Hefferan TE, Jewison DE, Wermers RA. Clinical spectrum of hypophosphatasia diagnosed in adults. Bone. 2013;54(1):21-27.