The Internet of Medical Things (IoMT) is a complex system of networked medical devices, traditional Information Technology (IT) systems, regulations, applications, and health data. These heterogeneous systems are particularly vulnerable to cyber-attacks because of medical device hardware constraints, lack of standardization, and limited security features. Periodic reviews of the scientific literature, including this research study, are important to explore risk assessment methodologies for the IoMT in response to medical device regulation and emerging cyber threats that exploit the vulnerabilities of these devices. This paper presents a systematic review of scholarly literature on security risk assessment methodologies for the IoMT published between 2019 and February 2024. Using forty-seven selected papers, this study reviews a diverse set of security risk assessment methods that mirror the complexity and heterogeneity of the IoMT.