Is it permissible to complete the discharge of semen by hand if one wakes up from a wet dream and its flow has stopped, but it remains in the urethra causing pain and harm?

Masturbation is forbidden due to its harms. However, if there is harm from the retention of semen in the urethra, and there is no cure for it except masturbation, then it is permissible to remove that harm. If the retained semen cannot be expelled except by masturbation, according to the report of a specialist doctor, and this is determined to be the course of treatment, then it is permissible to expel it by masturbation. But if the retained semen can be expelled by other permissible means, then those means must be used, and masturbation becomes forbidden.