The Five Types of Disc Herniation

The Five Types of Disc Herniation (that we know of!)

1. Dystrophic calcification secondary to chondroid degeneration of nucleus pulposus (NP), called a Hanson Type I. This causes mechanical stress on the outer annulus fibrosus (AF), leading to rupture of individual collagenous strands of AF and eventually full failure.

2. Fibrous degeneration occurs when fibers of disc split leading to accumulation of tissue fluid and plasma between them. Over time the mechanical pressure exerted by NP causes thickening of the AF dorsally, causing protrusion. (Hanson Type II).

3. ANNPE (Acute noncompressive nucleus pulposus extrusion) - this is normal NP that is exploded into the canal, usually during activity. Also called a traumatic disc herniation.

4. AHNPE (Acute hydrated nucleus pulposus extrusion) – An apparently normally hydrated NP that is compressive and often located ventral to the cord, often in the neck.

   1. Significantly more neuro deficits and less signs of cervical pain with AHNPE compared to other causes of cervical myelopathy.

5. FCE (Fibrocartilaginous embolism): a piece of NP that becomes dislodged and finds its way into the vasculature surrounding the spinal cord. This can be into venous or arterial blood vessels. The end result is an acute shift in blood flow at the level of the spinal cord.

Match the clinical sign with the type of disc herniation

A. Chronic, progressive ataxia progressing to paresis
B. Acute, non-progressive unilateral weakness affecting one leg, or one side (hemiparesis)
C. Acute, progressive, painful ataxia progressing to paresis in a chondrodystrophic dog
D. Acute non-progressive ataxia and paresis affecting both sides of the body (paraparesis or tetraparesis)
E. Acute, rapidly progressive tetraparesis and ataxia of all four limbs with minimal cervical pain

If you answered...
Type I: C
Type II: A
ANNPE: D
AHNPE: E
FCE: B

you are correct!

Based on the clinical picture, it can be very difficult to distinguish Type I from ANNPE, and AHNPE. Typically, type I is painful (but not always), and the other two are minimally to non-painful. 

Which of these require surgery?

Any disc herniation that results in compression of the spinal cord with associated clinical signs could be considered for surgical correction. This statement would then suggest that Type I, Type II and AHNPE could be surgically corrected. Therefore, any patient with signs of a progressive or painful myelopathy should be evaluated for diagnostic imaging (typically MRI) for possible surgical intervention whenever possible.

Bonus question:
Can you name two diseases that are commonly diagnosed instead of a type I or type II disc herniation? Scroll to the bottom for the answer!

Change is coming! Starting in September I will have new fees, and new availability.  I am happy to accommodate outside of these hours whenever possible so please reach out if you cannot find a suitable time using the online scheduler. ( https://barnesveterinaryservices.com/ )

New Hours (Starting September 8th)
Monday 11a-1p, 4-5p
Tuesday 3-4p
Wednesday 11a-1p, 2-4p
Thursday 2-4p
Friday 12-1p
Saturday 9-11a

Bonus Question Answer
 Meningoencephalomyelitis (a.k.a meningitis), and neoplasia. Keep these two on your differential diagnoses list when you suspect a disc herniation!!

The Genetics of Disc Herniation

What is the deal with chondrodystrophy, anyway?

Chondrodystrophic dogs are born to have short stature, and abnormal aging of the intervertebral discs. It's what makes a Dachshund or French Bulldog look like, well, a Dachshund or French Bulldog! I'm sure it comes as no surprise that there is a genetic reason why they look this way. But, did you know that someone has sorted out the genetic mutation that has been linked to chondrodystrophy and disc herniations?

What is the genetic mutation and what does it mean?

Several studies in 2019 (and earlier) looked at copies of 12-FGF4RG and 18-FGF4RG status in chondrodystrophic dogs and found that if a dog carried at least 1 copy of the 12-FGF4RG gene they were significantly smaller, younger and more likely to have radiographically calcified discs than those without. Furthermore, 12-FGF4RG was the only factor identified in multivariate logistic regression models that contributed to needing disc herniation surgery in mixed breed dogs. Mixed breed dogs? (You ask.) Yes, Dachshunds and French bulldogs, specifically, have such a high rate of carrying 1 or 2 copies of the 12-FGF4RG gene that it's impossible to say with the relative risk of disease is for these breeds with the mutation. In other words, if every Dachshund has the mutation is it actually related to disc herniation? Not sure yet. One study found that non-Dachshund and French Bulldogs had between a 5.1-15.1 fold increase of disc herniation if they had at least 1 copy of this gene. 

What do I do with this information?

If you have a neutered animal, nothing. It might predict the risk of disc herniation in that animal but that animal is already born, and presumably loved, so this information is not actionable. If you have a client considering breeding you may be faced with the results of this genetic information and asked the question above.  My opinion? There are specific breed risks so either read the published data on risk for the specific breed in question, or reach out to me and I'll gladly pass along the information. It's in a handy table, but not my data so I don't feel comfortable including it in the TidBit Tuesday mailer. If possible, breeders should try to breed dogs with zero or 1 copy to dogs with 1 or zero copies of the mutation to reduce it's presence in the breed. *This doesn't apply to Dachshunds or French Bulldogs for the above mentioned reasons!

Keep those chondrodystrophic dogs fit, healthy, and leading low impact lifestyles! It won't eliminate the risk of a disc herniation but it may make recovery easier. 

Batcher K, Dickinson P, et al. Phenotypic Effects of FGF4 Retrogenes on IVDD in Dogs. Genes (Basel) 2019; 10(6): 435.

Do you have a case you'd like to discuss with me? Feel free to email, text, or call me! I'm still trying to see mostly video consults whenever possible but I'm gradually increasing the live consults performed. Either way, I look forward to (continuing) to work with you!