If Dr Pillinger's article on developing a shared-care urology service (Guidelines in Practice May 2001, Vol 4(5): 45) I was puzzled by the reference to transabdominal ultrasound as a technique for assessing prostate size.
Secondly, in the absence of abdominal ultrasound, how reliable is assessment of prostate volume by digital rectal examination? I certainly would not be confident that I could tell whether a prostate was more or less than 40cc by this method.
The issue is important because of the criteria for choosing a 5alpha-reductase inhibitor rather than an alpha-blocker. When would it be acceptable to make this choice in the absence of a reliable measure of prostate size?
Dr Dougal Jeffries, GP, Isles of Scilly
Dr John Pillinger replies:
It is possible to assess prostate size with transrectal or abdominal ultrasound. New patients attending the community clinic undergo renal tract ultrasound, with transrectal ultrasound reserved for the investigation of those found to have an elevated age-related prostate-specific antigen (PSA) and/or abnormal digital rectal examination (DRE).
I agree that it isn't always easy to judge prostate size on DRE. Only the posterior portion of the gland is accessible to DRE, and therefore overall gland size may differ from the estimate derived by this method.
There are models representing different prostate sizes, ranging from 20cc through to 80cc, which are extremely useful for educational purposes.
As a general rule of index finger, if the prostate gland is felt to be the size of a mandarin on DRE, it is likely to be around 40cc or greater. Under these circumstances, provided that there are no red flag symptoms and signs, or complicating factors relating to co-morbidity and existing medication, you could prescribe a 5alpha-reductase inhibitor and review after 6 months.
If the patient's symptoms are particularly severe, you might use combination therapy initially to obtain faster relief, with a view to discontinuing alpha-blocker therapy on follow-up.
Should a patient whom you thought had a small prostate fail to respond to alpha-blocker treatment, a more accurate assessment of prostate volume would help you decide how best to proceed.
Dr John Pillinger, GP, Dorset, and urology clinical assistant, Royal Bournemouth Hospital NHS Trust