Slow-flow vascular malformations consist of abnormally formed veins, capillaries, lymphatic vessels, or a combination of these. They can cause pain, swelling, functional limitations, and concerns about appearance and may substantially affect quality of life. Bleomycin electrosclerotherapy (BEST) is an emerging treatment in which the sclerosant bleomycin is injected into the malformation and brief electrical pulses are applied to increase its local effect.

As treatment of slow-flow vascular malformations primarily aims to alleviate symptoms and improve quality of life, patient-reported outcomes are central to assessing treatment benefit. However, the available evidence on patient-reported outcomes following BEST is sparse and heterogeneous, and prospective data are particularly limited.

This prospective observational study follows children and adults undergoing BEST as part of routine clinical care at Copenhagen University Hospital - Rigshospitalet.

The OVAMA questionnaire will be used to assess symptoms and appearance in all participants before treatment and at the 6-month follow-up. Depending on age, additional patient-reported measures will assess health-related quality of life (PROMIS-29) and pain (VAS) during follow-up. For adults, the study will assess changes in lesion size by comparing magnetic resonance imaging (MRI) scans performed before treatment and at 6 months. Adverse events will be recorded throughout follow-up.

The study aims to evaluate whether patient-reported outcomes improve during the 6 months after BEST and to provide further information about treatment safety.