Wireless Medical Sensor Network (WMSN) consists of biosensors connected with each other implanted within the human body. It transmits data to remote medical centers. Medical professionals can access the sensors of the human body to inquire about his health condition remotely. Transmitting patient data over insecure wireless channels is a major challenge because health data are very sensitive and must not be disclosed to unauthorized users, so ensuring secure authentication and preserving anonymity is very important. To address this issue, many researchers have provided many protocols for WMSNs. An anonymous patient monitoring system using WMSN presented by Amin et al. and demanded that their system preserves mutual authentication, user anonymity and security against stolen smart device attacks. By studying thorough and in-depth analyses, we found that this system is attackable to privileged insider attacks and stolen smart device attacks. In addition, it does not protect user anonymity. Additionally, it fails to protect denial of service attack. Furthermore, it has an error in the password modification stage. To overcome the above limitations of the existing systems we have proposed an advanced and mask identity-based secure mutual authentication protocol using WMSN. An informal security analysis is performed, which shows that our protocol is secure against different types of attacks. Furthermore, in our proposed protocol we have used the BAN logic model to prove the correctness of the mutual authentication feature. In addition, it offers ease login, secure authentication and strong password change phases.