This above diagram shows an overall summation of how to diagnose pudendal neuralgia. There are many tests which can help in assisting to find out if the pudendal nerve is affected, like the PNMLT and the EMG test, but the only way to know for sure, if it is PN/PNE is through a pudendal nerve block.
Generally the first nerve block is at the ischial spine, because this is the most common point of entrapment. If the pain goes away then you can be 100% sure the pain is from an area served by the nerve at or below that point, or is from the nerve itself. To determine whether it's the nerve or not, various tests to rule out non-PN causes of pain must be done. These can be done before or after a nerve block. The diagram shows them done before, since most of these various tests are cheaper and more routine than a nerve block. It is estimated that 80 percent of the entrapments found in surgery are located at the ischial spine and 20 percent of the entrapments found in surgery are at the Alcock's Canal.
The ischial spine location has another advantage: it's about as high as you can go on the pudendal nerve before encountering the pudendal plexus. Above that, a nerve block would be somewhat useless, since that's where the pudendal nerve starts. See Pelvic Wall Blood Vessels and Nerves for where the pudendal plexus is.
If two or three nerve blocks with steroids (also known as corticoids) fail to give lasting relief at the ischial spine, the pudendal canal (Alcock's Canal) is tried. Other locations may also be tried. Dr. Robert cautions that:
"Two or three infiltrations are performed [at a single location]; this number should not be exceeded for fear of deterioration in the nerve trunk." - Source: PNE by Dr. Robert.
If an ischial spine nerve block has no effect on the pain, and the pain is in an area served by the pudendal nerve below the block location, then either the block was given incorrectly, or PN is not present. As Dr. Robert wrote in an email to a patient:
"The main problem arises for patients without any effect after blocks. I do believe that then they are not candidates for surgery." - Source.
However, most rules have exceptions. In a very small percentage of cases, a nerve block will not temporarily reduce or eliminate PNE pain. This can occur when the pudendal nerve has an unusual route, such the "rose petal" shape Dr. Robert found in one patient. There can be other reasons. Since even nerve blocks are not 100% reliable for testing, diagnosis must rely on a suite of tests.
