Thanks for reading the 29th edition of my sciatica newsletter. This newsletter tracks my research as I write a book about lumbar radicular pain!
Hi from a rapidly heating-up Houston!
This week I have mostly been reading around red flags and clinical reasoning for the project I’m working on with Rob Tyer.
But I did spend a bit of time on the 'assessment' section of the book.
Longtime readers of the newsletter might remember the paper by Foti and colleagues, who investigated 17 patients who had sciatica but didn’t have anything to explain it on their spinal MRI. Five of the patients had hypertrophied small hip muscles, which we might call 'deep gluteal syndrome', and four had... endometriosis plaques on their sciatic nerves.
How did those get there? I will freely admit my surprise when I first read this study. Although if I stop and think about it, the uterus and the sciatic nerve are pretty close together, it never really occured to me that the two would interact...
Sciatic endometriosis
Endometriosis is when the tissue of the inner lining of the uterus, the endometrium, grows outside the uterus. Sometimes, it grows in organs like the colon and the bladder. And endometrium can grow in the sciatic nerve too, mostly at the sciatic notch. When it does, it can cause pain that feels a lot like lumbar radicular pain.
Surgeons describe endometriosis damage to the sciatic nerve as dark blue or black "powder burn" lesions or deep red "flame" lesions.
The pain is right-sided two thirds of the time because on the left side, the sigmoid colon protects the sciatic nerve from the uterus.
It's not clear if sciatic endometriosis is common or not. On the one hand, since it was first described 80 years ago, only about 70 or so case reports have been published and not much else. On the other hand, if you ask people with endometriosis whether they have radiating leg pain, fully half of them will say yes! As I mentioned, Foti and colleagues found that four of 17 patients with unremarkable spinal MRIs had endometriosis plaques on their sciatic nerves. In another similar study, of 10 people with nothing on their lumbar MRI, two had sciatic endometriosis.
How to spot sciatic endometriosis
It seems safe to say that if a female patient has sciatica, we should ask if their pain is cyclical. Sciatic endometriosis is usually at its worst a few days before menses until a few days after. However, over time, as the endometrial tissue on the nerve becomes fibrotic, the pain can become less cyclical and more permanent. So if it’s been going on for many years, we should ask our patient if the pain was cyclical when it started.
What other clues can help us to spot sciatic endometriosis? There are some reports that it gets better during pregnancy. And people with sciatic endometriosis will usually, but not always, have particularly painful periods too. Buttock pain and pain with sitting are usually a feature, although of course this is common with spinal sciatica, too.
The next step for a diagnosis is a pelvic MRI.
Have you had any clinical experience with sciatic endometriosis? I'd love to hear from you! You can just reply to this email.
Til next time,
Tom
P.S. The free sciatica mini-course is going strong. If you want to sharpen up on the 'sciatica basics', sign up!
P.P.S. Here’s some photos from Houston’s ‘British Store’… I got some marmite and a curly wurly.