Answer
Vasc (40%)
--atherosclerosis + RF's
--venous leaks
--pelvic/perineal trauma (arterial/neuro trauma)
penile injury/ds
--trauma, priapism, peyronie's ds (scarring)
neurogenic causes
--radical pelvic surg (prostatectomy)
--pelvic/spinal cord injury
--MS, DM, PD, Alz, stroke
--pudendal n injury
hormonal
--hypogonadism
--hypo/hyperthyroidism
--pituitary tumour
--hyperprolactinemia
meds
--anti-HTN, SSRI, hormonal agents, protease inhibs, cytotoxic agents, H2 antagonists