Last month, we announced details of two new publications about enduring sexual dysfunction after the use of medications. We hope you found them interesting.
In both articles, we discussed a couple of studies from 1991 and 1999, in which neurophysiological testing showed that taking a serotonin reuptake inhibitor reduces genital sensation. We have previously mentioned these studies on the blog, but we wanted to draw attention to them in the PSSD literature as we believe they are very important.
Genital numbness or loss of genital sensitivity is one of the major hallmarks of PSSD. It happens to some degree to almost everyone who takes an SSRI or SNRI, and for some people it persists afterwards, or can develop when the person stops the drug.
In the studies mentioned above, small electrical impulses were used to produce a sensation at the genitals. These impulses were then reduced in intensity until the subject could no longer feel them, thereby providing a measurement of genital sensory threshold. This is different to nerve conduction studies which also use electrical impulses, but which involve the direct measurement of electrical signals to assess nerve function, rather than measuring the sensation that the patient can actually feel. Nerve conduction studies typically only assess large nerve fibres, meaning that the test can produce a completely normal result even though the patient might have problems with smaller nerves.
A disadvantage of using electrical impulses to assess genital sensation is that most people would be hesitant about subjecting their genitals to electricity. Fortunately, there are other methods of investigating sensory issues.
Turn up the heat
A few weeks ago, we asked whether there might be a link between PSSD, withdrawal and small fibre neuropathy. Could SSRIs and SNRIs be disrupting the normal functioning of small nerve fibres throughout the body, and could this be responsible for some of the problems seen in PSSD and withdrawal?
We think this is an important idea to explore and we are still keen to hear from those with PSSD or withdrawal problems who have been tested for small fibre neuropathy. We discussed several tests that can be used to investigate this condition including skin biopsy, corneal confocal microscopy and quantitative sensory testing.
Quantitative sensory testing is the collective term for a group of tests that are used to assess skin sensation. Devices which produce different types of stimuli are placed against the skin, usually on the hands or legs, and the patient is asked if they can feel the sensation. This could include temperature changes, pressure, vibrations, and others. Different stimuli activate different types of nerve fibres. For example, vibrations are useful for measuring responses in mainly large nerve fibres whereas changes in temperature are predominantly picked up by small nerve fibres.
The interesting point about quantitative sensory testing is that in addition to investigating conditions like small fibre neuropathy, it is sometimes also used in urology if a patient is experiencing genital numbness, or if they have erectile dysfunction that is suspected to involve a neuropathy. In these cases, the stimuli are applied directly to the genitals.
This raises the question of whether this type of testing could be used to measure the genital numbness in PSSD. The issue isn’t straightforward as there are various types of stimuli that could potentially be used and it’s difficult to know which ones, if any, would capture the abnormality. The complex nature of the genitals also adds a further complication – exactly which area of the genitals should you test?
We recently came across a 2003 paper by Bleustein et al, called “Quantitative somatosensory testing of the penis: optimizing the clinical neurological examination”. It looked at various types of stimuli at different genital locations to establish the best method of investigating for penile neuropathy. The study found that warm thermal thresholds at the glans produced the best results.
Thermal thresholds are assessed by placing a probe onto the body part being investigated. The temperature of the probe then increases or decreases slightly and the person is asked to report when they can feel the change, usually by pressing a button. Note that these are only moderate temperatures and not something that would cause burning or pain.
A single test
The findings of the Bleustein et al study may be very useful when it comes to PSSD. By narrowing down the list of possible tests to just one in a single location, it raises some interesting possibilities for research.
We know from clinical experience that most people will have a degree of genital numbing after taking a single dose of an SSRI, often within just 30 minutes of taking it. It would be fascinating to assess penile sensation in one or two healthy volunteers, then give them an SSRI and see how quickly this changes.
The technique could perhaps be used to assess genital numbness in a few PSSD sufferers. It might also be interesting to take a few people who previously used SSRIs, but who don’t have PSSD, and assess whether their genital sensation has returned to normal levels.
If we can find someone with experience of carrying out this test in a clinical or research setting, and we can interest them in PSSD, there might be an opportunity to explore these ideas – perhaps with a small pilot study. The advantage of testing thermal thresholds is that it’s quick, non-invasive, and is likely to be relatively inexpensive compared to something like fMRI.
If it turns out to be a useful method of objectively capturing abnormal genital sensation in PSSD patients, it might be particularly useful to those who have had difficulty in getting a diagnosis. It would also once again highlight the fact that SSRIs reduce genital sensation – something which seems to be consistently absent from conversations about SSRI sexual side effects.
Unfortunately, quantitative sensory testing isn’t available everywhere, and may be even rarer in a urological setting. It’s possible that it might be more commonly used in the US than in the UK, but it’s difficult to know for certain.
We need your help to find clinicians or researchers who might have experience of using quantitative sensory testing for genital issues, and particularly the testing of penile thermal threshold. One thing you could do is write to the urology department at hospitals in your area to ask if this type of testing is available. If you can find some hospitals where this is carried out, we can approach them about a possible collaboration. Obviously, if you have already undergone this type of genital testing for PSSD, we are very keen to hear about your results.
Recently, we have been receiving a lot of emails from people suffering from PSSD and similar conditions, asking questions that have already been covered in detail on the blog. We are concerned that people are not keeping up to date with our content, and that useful information is not being acted on. Continuing to answer the same questions is also taking up a lot of our resources.
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Quantitative sensory threshold testing
We have had an immediate response from one of our readers (SS) who has found 5 articles on QST and sexual functioning – all of which look very promising. Four are posted here and are worth downloading and chasing further.