A 40-year-old woman was referred to a tertiary metabolic bone clinic after sustaining bilateral atypical femoral fractures following a fall from standing height, while on denosumab.
At the time of referral, she was mobilising with crutches and required a wheelchair over longer distances. Her past history included previous low-trauma metatarsal fractures in 2005 at age 25, complicated by delayed healing. A CT scan of her ankle performed age 33 to assess ongoing ankle pain reported radiographic osteopenia, subsequently confirmed on DXA. Her general practitioner commenced weekly oral bisphosphonate therapy, but she experienced gastrointestinal intolerance and ceased it after 4 months. She commenced denosumab in 2014 at age 34 years, which she received regularly every 6 months for 4 years.
Other significant history included a seizure at age 28 for which she was prescribed sodium valproate. She denied any developmental or pubertal delay, early dental loss or any periodontal pathology, or family history of fractures.
In December 2018, aged 39 years, the patient sustained bilateral atypical femoral fractures (AFF) after a fall from standing height. A complete right femoral diaphyseal fracture was surgically fixed. A contralateral nondisplaced asymptomatic partial diaphyseal AFF was conservatively managed. DXA in February 2019 showed bone mineral density (BMD) at the lumbar spine 1.150 g/cm2 (T score +0.8, Z score +0.9) and left total hip BMD 0.730 g/cm2 (T score -1.7, Z score -1.4).
Routine pathology provided an important clue in making the diagnosis of a rare, but under-recognised, cause of osteomalacia. Case discussion will highlight locally available confirmatory testing and therapeutic options for this condition, which has seen significant advances in recent years.
This case illustrates an important differential diagnosis for fragility fractures in adults that is not to be missed due to treatment implications.