This is a diagnosis of exclusion in men presenting with dysuria and/or discharge, but tests for chlamydia and gonorrhea are negative.
There are a number of possible causes e.g. mycoplasma/ureaplasma infections but there are no specific tests for these and there is now way of knowing for certain.
Treatment is empirical with a single oral dose of azithromycin or a week of doxycyclin and it may be useful to treat any partners should this be a recurrent problem.
NB always remember the possibility of a UTI as well as an STI in young patients presenting with dysuria
Notes on Medicine/Surgery 