Cervical spinal arachnoid diverticulum (SAD)

Background: The spinal cord disease seen in Pugs affecting the front legs is called spinal arachnoid diverticulum (SAD). (These are sometimes mistakenly called arachnoid cysts in older literature, but unlike cysts, they are not closed, but constitute a bulge in an organ in the body.) The diverticulum presses on the spinal cord, thus causing walking difficulties and abrasions on nails and toes and sometimes wear on the top of the paw. Some Pugs get so bad that they eventually have to be euthanized, but Mauler et al. write that “the most characteristic clinical presentation is a moderate generalized proprioceptive ataxia [uncoordinated movements] without any signs of discomfort” (2014: 175).

The spinal arachnoid diverticula (SADs) affecting the forelimbs are found in the area of C1-T2, i.e. in the cervical spine and the beginning of the thoracic spine and are therefore called cervical (cervical = originates from the neck). SAD occurs between the spinal cord membranes, in the so-called subarachnoid space and can occur along the entire spine, but is most common in the neck and lower back/lumbar region. (Rohdin 2014: 229, 231; Mauler 2014: 176f; id. 2017: 850). When SAD occurs in the lower back/lumbar region, it can lead to the disease Pug myelopathy, which you can read more about here on the website.

The affected area at SAD highlighted with red arrows.

Mauler et al. have looked at a larger material of dogs of different breeds that had SAD. Their material consisted of records from 122 dogs, some of which had more than one SAD, so that the material comprised 125 SAD. Of these, 65 were located in the neck and 60 were located in the lower back. There were 21 Pugs included in the material. Of the Pugs, seven had a cervical SAD and 13 a thoracolumbar SAD. The last Pug had more than one SAD (Mauler et al. 2014: 175, 177, Table 1), but it is not clear where these were located. Thus, in Mauler et al:s material, we see that most Pugs had a SAD at the lower back (62%) while those with a SAD at the neck accounted for 33%.

The breed that had the highest frequency of SAD in Mauler et al:s material was the Pug, and then came the French bulldog, followed by the Rottweiler. The authors point out that even if the frequency is not high in each breed, you can still talk about a disease of the breed, unlike e.g. the German shepherd, where only single individuals develop SAD (Mauler et al. 2014: 177). Below is a table showing the frequency of SAD in the four mentioned breeds in Mauler et al:s material:

In a Swedish study by Rohdin et al. Pug owners answered questions about their Pug’s gait, and some of them had also submitted videos showing their Pug’s gait. The authors show in a table that 128 Pugs out of 336 (i.e. 38.1%) had abnormal abrasion of the nails. 80.5% of these 128 Pugs wore down the nails on their front paws, 4.2% wore down the nails on the rear paws and 15.3% wore down the nails on both front and rear paws. The researchers point out that this type of wear has emerged as a symptom of SAD in other studies (Rohdin et al. 2018: 4, Tables 2, 7).

In Mauler et al:s study, slightly more dogs had SAD in the cervical spine compared to the lower back, but the Pugs had more SAD in the lower back. In Rohdin et al:s study, most Pugs had abrasive damage to the front paws, which instead indicates that SAD in the neck is more common in Pugs than SAD in the lower back. Since Rohdin et al:s material is covered by many more Pugs, it is likely that it gives a better picture of what it looks like in the Pug population.

Abrasion on one of Nappe’s toes on the right fore paw.

In Mauler et al:s material, at two of the faculty’s the researchers received material from, 3.4 and 4.5%, respectively, of the Pugs that had been patients there had SAD (and this includes both cervical and thoracolumbar SAD). (From the third faculty, 16 dogs with SAD were included and none of them were Pugs.) In Rohdin et al:s material instead, a total of 30.7% had walking difficulties, and 80.5% of them had symptoms from the front legs (Rohdin et al. 2018: 3, 4, Tables 2, 7), which represents 24.7% of the entire Pug population in their study.

In addition to SAD being most common in Pugs in Mauler et al:s material, the disease in all breeds was most common in males. Of the 125 dogs included in their study, 97 males (78%) had SAD and 27 females (22%) (Mauler et al. 2014: 175f.). You see the same pattern in people, where especially men get SAD. The gender aspect is linked to possible causes for the development of SAD, as a factor may be hormonal. Mauler et al. write: “Because CSF volume has been shown to be influenced by hormones, a hormonal impact on SAD formation seems possible” (Mauler et al. 2014: 179).

In addition to the hormonal effects, the researchers have highlighted a number of possible causes for the development of SAD. One aspect is the hereditary and congenital one (see Rohdin et al:s study (2014) of seven Pugs that were related that all had SAD) and another is concomitant other diseases of the spine (Mauler et al. 2014: 175). In Mauler et al:s study, one-third (33.3%) of Pugs had other spinal diseases in the same region as their SAD, and in French bulldogs, almost two-thirds (61.5%) had other spinal diseases in the same region. The authors conclude that these other diseases may have contributed to the development of SAD (Mauler et al. 2014: 178, 180).

Biomechanical factors have also been identified as a possible cause of the development of SAD (Mauler et al. 2014: 175). SAD usually develop in the neck and the lower back/lumbar region, which are areas that are the most mobile in the spine. With regard to SAD in the lower back/lumbar region, researchers have suggested that defective vertebrae with underdeveloped or missing caudal articular processes in the area have led to chronic instability in the area, with the development of further disease as a result (Fisher et al. 2013; Driver et al. 2019). Read more about this under “Pug myelopathy (PM)”. In the studies I have read about cervical SAD, I have not seen any information on how common it is with defective caudal articular processes on the cervical vertebrae.

The symptoms of cervical SAD (i.e., when the forelegs are affected) appeared in Rohdin et al:s study at a median age of one year (2018: 4). In the study by Rohdin et al. of seven related Pugs, the symptoms occurred at the age of 3-4 months and manifested in such a way that the Pug began to drag the front paws and got wounds on the top of the paws. Symptoms worsened over time, causing the dogs’ coordination to impair and they sometimes fell over (2014: 230). In the case of these Pugs, the process seems to have been rapid, as three of them needed surgery already at the age of six or seven months. All three initially improved but one was euthanized after one month, and one after one year, both due to deterioration (Rohdin et al. 2014: 231f.).

The rapid progress that some of the seven Pugs showed does not appear to be the general outcome at cervical SAD. As we saw in the introduction, Mauler et al. write that “the most characteristic clinical presentation [of SAD] is a moderate generalized proprioceptive ataxia” (2014: 175).

Although cervical SAD is generally not aggressively progressive, Mauler et al:s study indicates that it progresses in most cases, as 95.3% of the dogs in their study with this type of SAD showed progression of the disease (2014: 178). Mauler et al. also conducted a study in which they examined the outcome of treatments at SAD. There they write that the dogs that were included in the study that were euthanized because of SAD lived an average of 152 months, i.e. 12.6 years, from diagnosis until they were euthanized (Mauler et al. 2017: 851). In Rohdin et al:s mentioned survey study, 47 Pug owners responded that their Pug had been euthanized or had died, and the most common cause was walking difficulties, accounting for 28.8% of these 47 Pugs (Rohdin et al. 2018: 6). However, their age does not appear in the study.

As noted above, Mauler et al. examined the result of various treatments of SAD. In this study, they used the same material as in the study I refer to above. The treatments they were looking at were medical and surgical. In the group receiving medical treatment there were 38 males and 12 females, and the Pug was the most common breed. 22 of these dogs had cervical SAD and 27 thoracolumbar SAD (Mauler et al. 2017: 850).

The medical treatment was mostly prednisone, but two dogs received carprofen, one gabapentin and one physical treatment alone. At the follow-up of the medically treated dogs, 43% of them had been euthanized due to their SAD while 40% were still alive. In the group of dogs that had undergone surgery (where Pugs may have included but it is not evident from the article), 13% had been euthanized due to SAD and 66% were still alive (Mauler et al. 2017: 851).

Mauler et al:s conclusion is that dogs with SAD that undergo surgery have a greater chance of improvement and survival (and regardless of whether the diverticulum was cervical or thoracolumbar, and regardless of whether it was a small or large breed) (Mauler et al 2017: 851). However, they point out that in other studies it has been shown that new SAD have emerged in the long term, which was not the case in their own study except in one case (Mauler et al. 2017: 852). Regarding the long-term prognosis, Alisauskaite et al. conducted a study in which they examined the results in the short and the long term after surgery of thoracolumbar SAD in 25 Pugs. They concluded that in the short term the prognosis was good, as 80% of the Pugs had improved. In the long term, however, 86% of the Pugs had deteriorated (Alisauskaite et al. 2018).

The picture the researchers give is that cervical SAD usually produce mild symptoms which, however, progress, but that some Pugs can also have more severe symptoms with wear on the top of the paw. The Pug is a breed where SAD is relatively common. There appear to be several reasons for the development of SAD, such as hormonal, hereditary and due to other spinal defects. It seems that surgery gives the Pugs a better chance of improvement than just medical treatment, but euthanasia because of SAD occurs even after surgery. It would be interesting to know if medical treatment increases survival compared to no treatment. Although in most cases the disease is mild, it causes a diminished quality of life for the Pugs and worries for their owners.

Goal: No Pug shall develop spinal arachnoid diverticula.

Strategy: The symptoms of cervical SAD usually occur early in life and thus it is possible to select Pugs with symptoms from breeding. Other spinal diseases often coincide with SAD, which is why it is important to have a prospective breeding dog’s spine examined using a CT scan or an ordinary X-ray. Only those Pugs that have a healthy spine, with no vertebral or soft tissue defects, should breed. The Pug also needs a normal length of back for improved back health. The Standard Pug today is compact and square, but we need to strive for the rectangular body shape of the “normal dog”, as breeders of old German Pugs and Retro Pugs do. Lindholm et al. write: “Excessive deviations from the normal dog’s exterior may mean that the breed has health concerns” (Lindholm 2015: 33, my transl. from Swedish). Read more about the Pug’s back health under “Hemivertebrae and other vertebral anomalies” and “Pug myelopathy (PM)”.

Sources and further reading:

Alisauskaite, Neringa et al. 2019. “Short- and long-term outcome and magnetic resonance imaging findings after surgical treatment of thoracolumbar spinal arachnoid diverticula in 25 Pugs”. Journal of Veterinary Internal Medicine 33, 1376–1383. doi: 10.1111/jvim.15470

Driver, Colin J. et al. 2019. “Magnetic resonance image findings in pug dogs with thoracolumbar myelopathy and concurrent caudal articular process dysplasia”. BMC Veterinary Research 15:182. https://doi.org/10.1186/s12917-019-1866-0

Fisher, Stephen C. et al. 2013. “Constrictive Myelopathy secondary to hypoplasia or aplasia of the thoracolumbar caudal articular processes in Pugs: 11 cases (1993–2009)”. Journal of the American Veterinary Medical Association 242: 223–229.

Lindholm, Åsa, Catharina Linde Forsberg and Ingalill Blixt. 2015. Hunduppfödning i teori och praktik. Svenska kennelklubben.

Mauler, D. A. et al. 2014. “Signalment, Clinical Presentation, and Diagnostic Findings in 122 Dogs with Spinal Arachnoid Diverticula”. Journal of Veterinary Internal Medicine 28, 175–181.

Mauler, D. A. et al. 2017. “Spinal Arachnoid Diverticula: Outcome in 96 Medically or Surgically Treated Dogs”. Journal of Veterinary Internal Medicine 31, 849–853.

Rohdin, Cecilia et al. 2014. ”Cervical spinal intradural arachnoid cysts in related, young pugs”. Journal of Small Animal Practice 55, 229–234.

Rohdin, Cecilia et al. 2018. ”High prevalence of gait abnormalities in pugs”. Veterinary Record. doi: 10.1136/vr.104510, 1–9.

Chapters in Strategies for the breeding of Healthy Pugs