We recently ran a couple of blog posts about the possibility of a link between post-SSRI sexual dysfunction (PSSD) and small fibre neuropathy:
The posts recapped some of the things we had previously discussed on the blog and also included new information about a Finnish PSSD support group – many of their members had undergone skin biopsy for small fibre neuropathy and tested positive.
Small fibre neuropathy is certainly consistent with many aspects of PSSD. Some people with small fibre neuropathy experience numbness in one area of the body while for others it’s more widespread – similar to PSSD. Although small fibre neuropathy is often described as involving tingling or burning sensations, particularly in the hands and feet, this isn’t the case with all sufferers.
There is an interesting paper from 2018 which described two patients with unexplained genital numbness (not related to medications) who tested positive for small fibre neuropathy. One of the patients had two biopsies – one near the ankle and another on the thigh. Nerve fibre density was much worse in the biopsy taken from the thigh. This suggests that small fibre neuropathy can be worse in a particular area of the body, in this case closer to the genitals, and may not conform to the typical burning sensation in the hands and feet.
Some people with small fibre neuropathy also report a variety of other symptoms, some of which overlap with problems experienced by people who have come off SSRIs such as fatigue, cognitive impairment, and urinary and gastrointestinal issues.
However, testing for small fibre neuropathy isn’t universally available and can be difficult to arrange. Patients who complain of skin numbness are often sent for nerve conduction studies instead. This is where small electric shocks are sent through the arms and legs to test how well the nerves conduct electrical signals. It predominantly assesses the function of large nerves and isn’t useful for investigating small fibre neuropathy. Unfortunately, neurologists sometimes misinterpret a negative result as meaning that the patient doesn’t have neuropathy.
An important point highlighted by the Finnish group is that even if patients have a skin biopsy, it requires expertise to interpret the results, and the age of the patient needs to be taken into account.
Dr Channa Hewamadduma is a neurologist with expertise in small fibre neuropathy, based in Sheffield, UK. He has spoken with Professor Healy and is happy to dedicate a small fibre neuropathy and skin biopsy clinic to 5 PSSD patients. The clinic happens on a Tuesday morning – the first Tuesday of the month.
Suitable patients need to be based in the UK – ideally not too old, and ideally on no other medications. You will need to get a printout of your medical history summary from your GP – basically to show you have no other conditions and no recent blood tests showing other problems. You also need to get your NHS number.
Men or women can take part. The group can be a mixture of both.
You won’t need a referral from your GP. Professor Healy would make the referral to Dr Hewamadduma. The testing will all be done on the NHS. However, you will need to pay for your own travel to and from the hospital in Sheffield, and as the clinic is on a Tuesday morning, this might involve staying overnight.
Dr Hewamadduma will aim to carry out the following investigations:
Assessment of sweat gland function using Impeto Medical’s Sudoscan device with feet and hand plates. This is a non-invasive procedure that evaluates the function of sweat glands by measuring the electrical conductance of the skin. You can read more about this on the Sudoscan website. It isn’t the same as nerve conduction studies (mentioned above).
Quantitative sensory testing (QST). This is a non-invasive procedure in which a probe is attached to the hands and feet. The probe gets warm or cold to varying degrees and you are asked whether you can feel it. This determines the threshold at which your skin can detect temperature changes. Here is a leaflet about QST from Sheffield Teaching Hospitals.
Skin biopsy at the ankle and maybe lower thigh. A few millimetres of skin is removed for testing in the laboratory to determine how many intraepidermal nerve fibres are present and whether this is normal for your age. Skin biopsy is regarded as the gold standard for detecting small fibre neuropathy.
Blood tests for genetic screening.
If you would like to apply for the testing, the first step is to complete and return this form with details of your case. The cases will be reviewed for suitability, and you will then be contacted for any further information such as your NHS number and the printout of your medical history summary.
The aim is to get people into the clinic for the first Tuesday in January or February 2023. Five people would take up one whole clinic.
It is very generous of Dr Hewamadduma to offer one of his clinics for PSSD patients, and it will only go ahead if enough people come forward to take part.
If there are any pointers from the testing, the results will be written up into a research paper and published in a medical journal. Obviously, your details will be anonymous with no indication of who you are. Dr Hewamadduma would also be willing to write a grant to make it possible to test a further 25 people or so.