Osteogenesis imperfecta is an uncommon bone disorder caused by mutations in type I collagen involved in bone matrix leading to increased fracture risk. There are several sub-categories within OI, with OI type I being the most common and mildest form. Women with OI considering pregnancy need to be aware of bone loss and fracture risk, particularly with lactation.
We report a case of a 38-year-old female with OI type I who presented with vertebral fractures (T7, T8 and T11) four months following twin delivery and post-partum lactation. The patient had significant debility resulting from her fractures with pain and inability to lift her children. Following endocrine review, she weaned breast-feeding but represented within weeks with further pain - MRI demonstrated new T12 and L1 fractures.
Dual-energy X-ray absorptiometry scan (DXA) revealed reduced bone mineral density (BMD) of 0.712g/cm² at the lumbar spine (LS) (T-score of -3.0), and 0.662g/cm² at the left total hip (LTH) (T-score -2.3). She received intravenous zoledronic acid 5mg. However, 12 months after her infusion, she experienced further thoracic pain after lifting and an MRI showed a new T7 fracture. High resolution peripheral quantitative computed tomography showed severe generalized microarchitectural deficits with reduced total, cortical and trabecular volumetric BMD in both the radius and tibia. Cortices were markedly thin with low trabecular bone volume fraction, trabecular number, as well as increased separation. The patient commenced teriparatide 20mcg daily for 12 months. Repeat DXA following teriparatide demonstrated a significant BMD improvement of 28.0% at the LS (0.912g/cm², T-score -1.2), and 11.6% at her LTH (0.739g/cm², T-score -1.7).
Bone loss with lactation is an important consideration for women with OI considering pregnancy. Women with OI should be assessed by an endocrinologist prior to conception to optimise bone health and have an individualised plan to support women and mitigate risk.