SAT-576 Possible Involvement of Thyroid Function in PCSK9 Inhibitor Therapy

INTRODUCTION Proprotein convertase subtilisin kexin type 9 (PCSK9) inhibition is an effective strategy for lowering plasma LDL-cholesterol and enhancing the LDL-cholesterol lowering ability of statins. PCSK9, a serine protease that binds to the LDL receptor promoting its degradation, is an important regulator of LDL metabolism. In addition, LDL-cholesterol is also controlled by TSH and thyroid hormones via PCSK9. TSH has received increasing attention as being closely associated with increased LDL-cholesterol level and higher atherosclerotic risks. In vitro study, the effects of TSH on hepatic PCSK9 expression in HepG2 cells were reported (1). I here report a case of transient hyperthyroidism secondary to PCSK9 inhibitor therapy. This case highlights the involvement of thyroid function in PCSK9 Inhibitor therapy. CLINICAL CASE A 65-year-old man had a weight loss of 6 kg (13 lbs.) in 4 months, accompanied with fatigue. He had a past history of myocardial infarction and his LDL was 83 mg/dL by 2.5mg of rosuvastatin and heart rate was controlled by 10mg of carvedilol. Six months ago, he started a PCSK9 Inhibitor therapy with 140mg of evolocumab every 2 weeks for 6 weeks. He had no preceding viral illness and denied anterior neck pain or tenderness. His height was 1.53 m, weight 52.6 kg (115 lbs.), and body mass index (BMI) 22.46 kg/m(2). His thyroid was not enlarged and non-tender without clear palpable thyroid nodules or neck lymph nodes. Hyperthyroidism was suspected and confirmed by thyroid function tests: TSH was less than 0.0005 μIU/mL (normal 0.35–4.94), and free T4 1.830 ng/dL (0.70–1.48). Graves’ disease was considered, and thyroid antibody tests performed. Thyroid peroxidase (TPO) antibody titer was less than 9 IU/mL (<9), and TSI 141% (<120%). To confirm the diagnosis of this hyperthyroid patient, Technetium-99m uptake and scan was done which showed uptake of 0.8% (0.5–7%). After careful observation for 2 months with 5mg of carvedilol, he turned asymptomatic and free T4 lowered to 1.480 ng/dL and TSH remained less than 0.0005 μIU/mL. CLINICAL LESSONS I here report a case of transient hyperthyroidism secondary to PCSK9 inhibitor therapy. There has been no report of hyperthyroidism induced by PCSK9 inhibitors. Immunological influence of anti-PCSK9 therapy on thyroid is unknown. In this case, the decrease of TSH due to hyperthyroidism was considered to reduce hepatic PCSK9 expression, leading to additive effect to PCSK9 inhibitor. PCSK9 inhibitors may modify the effects of hyperlipidemia treatment by causing changes in thyroid function. When using PCSK9 inhibitors, follow-up of thyroid function should be considered. This case highlights the involvement of thyroid function in PCSK9 inhibitor therapy. Reference (1) Gong, Y., Ma, Y., et al. Thyroid stimulating hormone exhibits the impact on LDLR/LDL-c via up-regulating hepatic PCSK9 expression. Metabolism. 2017;76;32–41