Know your spinal cord – Tabes dorsalis

We’ve made it to day twenty-four of fun spinal cord knowledge! If you’re just joining us, we have a whole new neuroanatomy category for you to find all the posts in this series in reverse chronological order. If you want to know everything, then you’ll want to start at the beginning with the medullary pyramids. Over the past week in our series we’ve been talking about spinal cord disorders and today we are looking at something called tabes dorsalis, let’s begin!

Yesterday we covered Lichtheim’s disease, which came with a little warning about the dangers of recreational nitrous oxide use as well as making sure you get your B12. Tabes dorsalis comes with its own fun warning, which we will get to at the end, but for now let’s take a look at what tabes dorsalis does.

To be fair, the name gives it away, dorsalis meaning dorsal. So just from the name we can tell that this affects the dorsal portion of the spinal cord. Like Lichtheim’s, tabes dorsalis is a neurodegenerative disease. Specifically it causes demyelination of the dorsal columns and dorsal roots of the spinal cord. Now, if you haven’t read yesterday’s post, demyelination means removal of the fatty sheath that covers axons which increases the speed of the electrical signal. This means tabes dorsalis is going to affect a persons sense of touch, proprioception (knowing where your body is in space), vibration, and discriminative touch (the part of touch that tells you where on your body the touch is coming from). The image below highlights the symptoms of tabes dorsalis.

Unlike Lichtheim’s, symptoms might take decades to appear. Those symptoms might start off as weakness, shooting/burning/pricking pains in the extremities, loss of coordination, episodes of intense pain/disturbed sensation, urinary incontinence, and even things like dementia, deafness, and loss of vision. Basically a lot of widespread neurological issues that are all very bad. Let’s look at a transverse section of a stained spinal cord slice (below) so you can see the damage this causes.

The manifestations of tabes dorsalis are due to chronic inflammatory disease of the dorsal roots (arrows) and ganglia with associated degeneration of the posterior columns as seen in this section of lumbar spinal cord stained for myelin.

On the skeletomuscular side of things, we see decreased muscle tone due to the destruction of the sensory limb responsible for the spindle reflex. As you might expect, deep tendon reflexes are also diminished or absent (like the patellar reflex). This also leads to something called an ataxic gait, which is a failure of coordination or irregularity of muscular action of the limbs.

Left untreated, these symptoms can (and do) get worse. There is treatment and it’s super effective! Unfortunately even with treatment, the neurodegenerative side effects persist. This means early detection and treatment are key to prevent this sort of progression. There are blood tests that can be done, but if symptoms occur even an MRI will pick up the degeneration as shown in the image below which I’ve added a red arrow to highlight the region. However, we haven’t covered the cause of tabes dorsalis, which means now it’s time for the PSA portion of our post!

Degeneration of the dorsal tracts of the spinal cord caused by tabes dorsalis (red arrow) as seen in an MRI scan.

The cause is an advanced syphilis infection, which we can treat people! Remember, early detection is the key here. While syphilis is becoming antibiotic resistant, making it more difficult to treat, it is one of the few STD’s (sexually transmitted diseases) that are treatable. Yes, you can get syphilis other ways, but sex is the common cause so today’s PSA (public service announcement) is, use protection and get tested! To help prevent the spread of misinformation, I should point something out. No, you cannot contract syphilis through toilet seats, daily activities, hot tubs, sharing eating utensils, or sharing clothing with an infected person. Syphilis doesn’t survive outside of the body that well, which is good news or it would probably more commonly occuring.

You now know all you ever wanted to know (probably) about tabes dorsalis! Go impress your friends, they will love knowing this stuff. This brings us to tomorrow’s topic… well unfortunately tomorrow is my biweekly “critical” review paper on a spinal cord topic. I say unfortunately becuase I’m not really ready for it, but deadlines and what not. So you’ll get to read that tomorrow as another brief interruption in our knowing your spinal cord series. As for the next topic in the series, well you’ll have to wait to find out (I actually know, I’m not just saying that to avoid telling you).

Until next time, don’t stop learning!