Is it required to routinely check fibrinogen level in patients with rheumatic diseases on tocilizumab? Case-based review.

Tocilizumab (TCZ) may rarely cause hematological side effects including neutropenia and thrombocytopenia. TCZ is essentially expected to lower the fibrinogen levels to stay within the normal range, but TCZ-induced hypofibrinogenemia has been rarely reported in literature. Although it may remain asymptomatic, hypofibrinogenemia has clinical significance owing to the tendency of the condition to result in bleeding. A 65-year-old female patient with known polymyositis was, approximately 20 years after the diagnosis was made, examined due to elevated acute phase reactants leading to the diagnosis of giant cell arteritis (GCA) and TCZ treatment was initiated as she had former steroid-induced osteoporotic fractures. 1 month after the initial dose of intravenous (IV) TCZ, she presented with ecchymosis and was detected to have hypofibrinogenemia. Following the administration of the second dose, hypofibrinogenemia was detected again. In this review, we have analyzed this patient in addition to the cases in six other articles of TCZ induced hypofibrinogenemia which we found out based on our search strategy. Our aim is to point out a rare side effect of TCZ, hypofibrinogenemia, thus to emphasize a possible bleeding disorder and discuss probable underlying mechanisms.