Haemorrhagic cystitis: a common but under-recognised complication
A study conducted at the Queen Fabiola University Children's Hospital sheds light on a painful complication affecting one in seven paediatric transplant patients.We spoke with Dr Pauline Mazilier, a paediatric haematologist at the Children’s Hospital.
Haemorrhagic cystitis is an inflammation of the bladder, accompanied by blood in the urine. It can cause intense pain, especially during urination, and in some cases, may lead to severe anaemia requiring transfusions.
Among children who have received a bone marrow transplant, some develop a complication that is both discreet and disabling: haemorrhagic cystitis. Pain, blood in the urine, prolonged hospital stays… This condition affects one in seven transplant recipients but remains poorly understood.
Dr Pauline Mazilier, Head of the Bone Marrow Transplant Unit at the Queen Fabiola University Children's Hospital (Brussels), shares the insights gained from a study carried out with her colleagues.
What is a bone marrow transplant in children, and in what context is it offered?
Haematopoietic stem cell transplantation, often referred to as a bone marrow transplant, is used to replace bone marrow that no longer functions properly. It is offered to children suffering from serious blood disorders, immune system diseases, or certain cancers.
At the Children’s Hospital, these transplants are performed within the Paediatric Haemato-Oncology Department.
You focused on a specific complication: haemorrhagic cystitis. What exactly is it?
It is an inflammation of the bladder, with blood in the urine. It can cause intense pain, particularly when urinating, and in some cases, may result in severe anaemia requiring blood transfusions.
This complication can have two main causes: either the toxicity of certain treatments, such as chemotherapy administered prior to the transplant, or a viral infection, particularly by the BK virus – a virus that is normally harmless but can become pathogenic in immunocompromised patients.
I focused on this topic as part of a specialised training programme because it is a complication we encounter regularly. It can be severe for the patient, and there are currently no established treatment guidelines.
What were the findings of your study at the Children’s Hospital?
We reviewed the medical records of 163 children who underwent transplantation between 2007 and 2022. Around 15% developed haemorrhagic cystitis, confirming the high frequency of this complication.
In two-thirds of cases (66.7%), it was linked to reactivation of the BK virus due to post-transplant immunosuppression. This means the infection was not acquired externally, but rather a silent reactivation of a dormant virus.
We found no correlation with age, donor type, or conditioning regimen. However, one clear risk factor emerged: the presence of severe acute GvHD (graft-versus-host disease), which requires intensive immunosuppressive treatment. These children appeared to be the most vulnerable.
What is the current management? Are there effective treatments?
There is no standardised treatment protocol. We always begin with supportive care: aggressive hydration to dilute the urine and flush out clots.
We also use cidofovir, an antiviral agent active against the BK virus. It is the reference treatment, but it is not easily accessible, not reimbursed in Belgium, nephrotoxic, and of limited effectiveness since it does not specifically target the BK virus.
In the most severe cases, we resort to intravesical instillations, hyperbaric oxygen therapy (in collaboration with the Queen Astrid Military Hospital in Neder-over-Heembeek), or arterial embolisation – a more invasive procedure to stop bleeding.
What are the prospects for improvement?
The real challenge today is to better understand what works. Treatments are available, but they are not compared systematically. We lack robust data and larger patient cohorts.
That is why we are seeking to collaborate with other centres, notably through the Belgian Paediatric Transplantation Working Group (BSPHO) and the Société Francophone de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC).
A collaborative and recognised study
The study was conducted at the Children’s Hospital with contributions from Drs Laurence Dedeken, Pierluigi Calo, Safiatou Diallo, Laure Kornreich, Stéphane Luyckx and Christine Devalck, in collaboration with Dr Eléonore Powis (Queen Astrid Military Hospital, Neder-over-Heembeek) and Dr Adriano Salaroli (Jules Bordet Institute, Anderlecht).
Dr Mazilier presented her findings at the EBMT 2025 congress (European Society for Blood and Marrow Transplantation), a major event in the field of transplantation.
See the scientific poster: Présentation EBMT 2025
Watch the video: LinkedIn –Lien LinkedIn – Medimix x EBMT