Klippel-Trenaunay syndrome (KTS) is a rare slow-flow congenital vascular disorder with an incidence of 1:100,000. 1 , 2 KTS is classically characterized by a clinical triad of capillary malformation, venous malformation, and bony or soft tissue hypertrophy. RAD50 and POLE genes act directly on deoxyribonucleicacid (DNA) and genome stability. Although distinct from the more studiedphosphatidylinositol-4,5-bisphosphate3-kinase catalytic subunit alpha (PIK3CA)gene, RAD50 and POLE genes coexist as a deficient gene in few vascular malformations and papillary thyroid carcinoma (PTC).

This is a case of a 7-month-old Filipino female patient clinically and radiologically diagnosed as KTS presenting with multiple capillary malformations and left limb length-girth discrepancies. Dermoscopy showed various vessel patterns in all affected areas. Soft tissue ultrasound and magnetic resonance imaging/angiography (MRI/MRA) of the left extremities revealed subcutaneous capillary malformations, hypertrophy of the subcutaneous structures and compartment muscles. Strong family history of PTC was elicited and genetic sequencing revealed detected RAD50 and POLE genes. She was treated using the mammalian target of rapamycin inhibitor sirolimus with careful monitoring of trough levels and radiographic tests. A significant outcome one year post-sirolimus revealed no abnormal vessels on ultrasound, a lesser degree of hypertrophy and capillary malformations were no longer appreciated in MRI/MRA of left extremities. Port-wine stains (PWS) and affected limbs showed a decrease in erythema and growth rate during the treatment period.

KTS detected with RAD50 and POLE genes successfully treated with sirolimus with trough-level monitoring. Radiographic evaluation and regular anthropometric assessment remain valuable in the diagnosis and monitoring.