Methotrexate-Induced Toxicity After Ultrasound-Guided Intragestational Injection in a Patient with Caesarean Scar Pregnancy—A Case Report

<i>Background and Objectives</i>: Caesarean scar pregnancy (CSP) is a rare form of ectopic pregnancy in which the early pregnancy implants at the site of the uterine scar. Methotrexate (MTX) in lower doses can be used to treat CSPs. However, MTX administration is associated with a spectrum of side effects that include hematological toxicities. This case report presents a CSP treated with an intragestational injection of MTX and subsequently developed pancytopenia. <i>Materials and Methods</i>: A 23-year-old woman at six weeks and six days of pregnancy was referred as a potential case of CSP. After establishing the diagnosis, she was treated with a transvaginal ultrasound-guided intragestational administration of 80 mg MTX (adjusted to 50 mg/m² body surface area) under sedation. <i>Results</i>: On day four after the MTX injection, she developed oral ulcers, fever, and pruritic phlyctenular maculopapular rash. Subsequently, the patient developed febrile neutropenia and was admitted to the Intensive Care Unit. On day six, a subsequent exacerbation of the rash was observed with the formation of blisters and purplish spots with concurrent odynophagia and sialorrhea. Ultimately, the patient developed pancytopenia due to bone marrow suppression. Fifteen days after MTX administration, the patient recovered and was discharged from the hospital hemodynamically stable, afebrile, with dropping β-hcg levels, and in good clinical condition. <i>Conclusions</i>: Although methotrexate administration is the preferred option for the treatment of cesarean scar pregnancies, clinicians should be aware of the fact that its use entails potential risks, even when it is used locally. To our knowledge, this case is the first description of pancytopenia due to bone marrow suppression following a single low dose of intragestational methotrexate injection.