Homozygous Factor V Leiden Complicated by Heparin-Induced Thrombocytopenia: A Case Report.

Homozygous factor V Leiden (FVL) is a rare condition, occurring in 0.2% of the white population. This disease's rarity and aggressive pathophysiology can represent a challenge even to the most experienced clinicians. We report a case of a 35-year-old white man, who presented to the emergency department with a 1-week history of bilateral thigh swelling and pain. His past medical history included homozygous FVL mutation complicated by multiple venous thromboembolic events in the last decade, recent inferior vena cava (IVC) filter placement, diabetes mellitus type 2, and hypertension. Despite being trialed for different anticoagulation therapies over 10 years, including warfarin (international normalized ratio (INR) goal 2 - 3), rivaroxaban, and dalteparin, he continued to thrombose. On admission, while on a therapeutic dose of dalteparin, he was diagnosed with extensive acute deep vein thrombosis involving the bilateral femoral and iliac veins, extending proximally to his IVC filter to the renal veins, and pulmonary embolisms in the bilateral lower lobes and right middle lobe. A heparin drip was initiated, and he developed progressive thrombocytopenia over 96 h. Heparin was discontinued, and he was switched to argatroban. He was diagnosed with heparin-induced thrombocytopenia (HIT) with positive anti-platelet factor 4 (PF4)/heparin antibodies and a serotonin release assay. His platelets trended up to normal levels 5 days after heparin discontinuation. He underwent multiple thrombectomies, thrombolysis, and angioplasty of the abdominal and lower extremity veins. The IVC filter was removed. Secondary thrombophilia workup was remarkable for a positive lupus anticoagulant, which had been negative in the past. The patient was bridged to warfarin, discharged with a higher INR goal of 3 - 3.5, and continuously monitored factor II activity (goal 15-30%). This case illustrates a patient with recurrent episodes of thromboembolic events because of homozygous FVL. This condition's pathophysiology and therapeutic approach has been well studied in heterozygous carriers; however, homozygous individuals represent <1% of cases. Given the rareness of the disease, there are no well-established therapeutic guidelines, and long-term anticoagulation remains the therapeutic cornerstone. This case emphasizes the challenges in managing patients with homozygous FVL and complications that can occur due to this gap in the literature. We suggest further case reports and research studies to shed light on this serious condition and its lifetime complications.