Acquired von Willebrand's syndrome caused by primary hypothyroidism in a 5-year-old girl.

Background Acquired von Willebrand's syndrome (aVWS) associated with hypothyroidism is rare in children and more often diagnosed during the peripubertal period in the context of Hashimoto's thyroiditis. Case presentation A 5-year-old girl was referred to the paediatric haematology unit for rectal bleeding, anaemia and prolonged activated partial thromboplastin time (aPTT). Her developmental and learning skills were normal. The physical examination revealed severe short stature (height SDS: -3.6) with overweight (body mass index SDS: 1.8) and clinical sign of hypothyroidism. Laboratory investigation revealed aVWS type 1 associated with severe primary hypothyroidism. Anti-thyroid antibodies were negative and thyroid ultrasound found thyroid hypoplasia in favour of congenital hypothyroidism. Restoration of euthyroidism was associated with increased growth velocity and normalisation of coagulation parameters. Conclusion This report highlights the importance of excluding an underlying pathology (including hypothyroidism) in children with suspected VWS, even in young age.