Background Pediatric Antiphospholipid Syndrome (ped APS) is the most common acquired condition of increased blood clotting in developmental age.

Objectives This case report describes a 13-year-old patient with primary ped APS.

Methods The patient presented with a history of transient visual disturbance in 2019, exhibiting a limited visual field in the left eye. MR brain imaging and EEG showed no abnormalities.

In 2021, the patient experienced headaches and swelling of the face and neck. Physical examination revealed dilated collateral circulation vessels on the chest.

Angio CT of the head, neck and chest revealed extensive thrombosis of the neck vessels involving both internal, external, subclavian, brachiocephalic veins up to superior vena cava. On the right side, the thrombus extends higher, visible in the lumen of the sigmoid sinus. On the left side, the lesion started in the extracranial segment of the internal jugular vein with extensive collateral circulation.

Abdominal ultrasound excluded thrombosis while ECHO yielded normal results.

Laboratory tests ESR, CRP with normal limits, PLT 108 thousand/mm3. Coagulation system tests revealed elevated D-dimers, APTT, INR.

Tests for thrombophilia showed no evidence of Leiden mutation of factor V gene, but the abnormal result was obtained for the presence of variant F2:c.*97G>A in a heterozygous pattern mutation G20210A.

Additionally, ANA - 1: 640, high levels of anti-cardiolipin antibodies (aCL) IgM, IgG, anti- B2GPI IgM, LAC were detected, anti - dsDNA, anti-Sm were not detected. Complement components C3, C4 were with normal limits, BTA test results were negative.

Results According to Revised APS Criteria (2006) and ACR/EULAR APS Criteria - ped APS was diagnosed. The patient did not meet the criteria of SLE or thrombosis associated thrombophilia.

Treatment with low-molecular-weight heparin in a therapeutic dose was initiated, followed by the use of warfarin.

Follow-up tests after 2 years revealed low titer of anti-cardiolipin antibodies IgM, IgG, positive LAC, ANA 1:320.INR 3.6, persistence of anti- B2GPI IgM antibodies.

Conclusion In the diagnosis, consideration was given to SLE-like syndrome, but the significant improvement with only anticoagulants speaks in favor of APS. Further follow-up tests are necessary for SLE due to the presence of ANA.