Received: 18 March 2019
Accepted: 20 May 2019
First Online: 28 May 2019
Ethics approval and consent to participate
: The study was approved by the Ethical Committee of Nihon University School of Medicine No informed consent was required because this was a retrospective observational study using anonymized archived data from a clinical database and did not compromise anonymity or confidentiality.
: Not applicable.
: The authors declare that they have no competing interest.