SPINOCEREBELLAR ATAXIA
Late Onset Ataxia
Spinocellebellar Ataxia (SCA) is a condition, which starts to affects puppies from the ages of 4 –9 months approximately.
This condition should not be confused with Cebellar Ataxia, which is
early on set, which we are told has been researched and that the 2 conditions
are totally unrelated.
These early
symptoms tend to be intermittent in that the dog may appear perfectly normal
some days but not others. Some of the early signs area unsteady drunken like
gait, the puppy usually does not like slippery floors and they are unwilling to
go upstairs.
As the disease
progresses the limbs are lifted in an exaggerated manner, often described as
goose-stepping. The puppy may become unsteady, falling over occasionally.
Throughout the period of the disease the dog appears to suffer no pain, has a healthy appetite, has normal bodily functions. It will play and enjoy daily walks as any normal dog would. In some cases the dog will stabilise when they reach about 18 months old but the symptoms do not completely go away and the dog will have the condition all of its life. Some physiotherapy/swimming does seem to help the symptoms but this does not eradicate it. Dogs can go on to lead a normal happy family life. Here is a video of a JRT with SCA http://www.youtube.com/results?search_query=jrt+ataxia&search_type=
It is not certain what the mode of inheritance is, there are 2 likely traits:
It could be caused by Autosomal Recessive gene, which means is can happen to either sex and both parents have
to carry the gene before an affected puppy will be produced.
Affected x carrier = 50% affected 50%
Carriers
Affected x Clear =all Carriers
Carrier x Carrier =25% clear 25% affected 50% carriers
The other thought is that is could be a Polygenic mode of inheritance
Polygenic, means many genes. Let’s say an animal needs four genes to be affected call them ABCD. One parent carries ABOO, and the other, OOCD. The offspring could inherit ABOO, ABCO, AOOO, OBCD, OBOD..........OOOO. 64 possible combinations. There is a 1:64 chance an offspring will be affected, 62:64 of being a carrier, and 1:64 of being totally clear. Nobody knows how many genes are involved in SCA. The more there are, the harder they will be to identify. They may not even be on the same chromosome!If this disease is polygenic it will be very difficult to find a marker gene an example of a disease which is polygenic is Hip Displasia.
What can we do?
We
can start to gather information about the condition at any time. Owners
of affected dogs (or possible affected dogs) are encouraged to contact either
Cathryn Mellersh (cathryn.mellersh@aht.org.uk) or Luisa De
Risio (Head of Neurology at the AHT) (luisa.derisio@aht.org.uk).
For a genetic study it will be very important that dogs we classify as
'affected' are all really affected with the same condition, so a robust
diagnosis is very important. But in the first instance videos of affected
dogs can be very useful and Luisa will be able to advise owners of affected
dogs on the best way to provide a video.
A Layman’s Guide to Primary Lens Luxation (PLL) in dogs.
Description:
This is a condition where the lens is partially or fully dislocated from the threads that hold it in position within the eye. These tiny threads, sometimes called ligaments are known as zonules and it is they that weaken and break causing this condition. Using normal ophthalmic instruments (such as your own vet may possess) it is difficult to even see these small threads. What the experienced ophthamist (not your own vet) should also be looking for is a wobble in the lens as the dog moves its head around. This indicates that the zonules are becoming weak. Weak zonules are called subluxated, completely detached (luxated).
Unfortunately, each eye can behave differently, so a rapid onset on one eye, may or may not lead to a gradual (and predictable) onset with the other. As this appears to be a genetic defect in dogs, then it is almost certain that eventually both eyes will be affected.
There are two directions in which the lens can go; forward and backward. Forward is called anterior luxation and backwards is call posterior luxation. The lens can also detach at an angle which can cause bruising of the cornea (edema of the cornea). This causes the cornea to loose its transparency in the area of contact. This may or may not be permanent.
What to look for:
Forward is the usual way. The iris, the coloured part of the eye, surrounding the pupil (the normally dark spot in the centre of the eye) can be almost invisible, being fully open and unable to contract even in strong light. The pupil is consequently very large revealing the greenish hue (in fact, a reflection) from the back of the eye, the sort of colour exhibited by animal eyes when illuminated at night.
In addition, the eye might appear slightly swollen and the dog may have difficulty holding his eye open. These are VERY BAD signs. They indicated that pressure has already built up in the eye, possibly to damaging levels.
Other symptoms can be shivering – due to pain. Some dogs have a habit of shivering for no reason in any case but it is worth checking the eyes if he/she is shivering for no apparent reason.
If the lens goes backwards, there may not be any symptoms and what the prognosis may be. However, there is the possibility that the lens could go forward at sometime and cause glaucoma and the other conditions mentioned.
What happens:
When the lens goes forward in the eye, it usually blocks the flow of fluid (aqueous humour) which is continually produced in the normal eye by a ring of tissue (the cilary body) between the iris and the lens. The majority of this fluid normally flows out of the eye. Because the fluid cannot drain away, a condition arises which can cause irreparable damage to the eye due to the build up of pressure. This condition is known as glaucoma.
Nowadays, pressure (tonometry, the measurement of eye pressure) is easily measured with a small hand held digital (no moving parts!) pressure gauge (a tonopen) held against the front of the eye. Normal pressure should be in the range of 15 to 25 torr (mm of mercury) but can reach as high as 60 (with glaucoma). That is over one pound per square inch.
At the back of the eye is the light receptive area. These cells (rods and cones) are mounted in a structure called the retina, which is held on to the interior wall of the eye. The blood flow and information from the light sensitive cells pass out of a central area in the back of the eyeball, which contains the optic nerve (which transmits the information from the cells). Pressure build-up in the eyeball can cause permanent damage to the optic nerve itself and constrict the blood flow, which can lead to the death of the light sensitive cells. A consequence of this is that the retina detaches from the eyeball. This can be seen eventually by examination of the eye, thought it might take some months to happen. Partial detachment can also occur. Detachment can be progressive. The amount of detachment relates to the level of vision available to that eye.
This detachment is not in anyway painful to the dog. However, if glaucoma is allowed to remain untreated for as little as six hours, then you dog will be fully blind in that eye. It is important that the dog is immediately seen by a vet who is fully knowledgeable in this subject (See above list). Most vets aren’t, or don’t appreciate the seriousness of the situation. This is an ACUTE (requires urgent attention)condition not CHRONIC (slow).
The treatment:
It was originally understood that the only treatment was an immediate operation to remove the lens. However, now there are drugs, which, if given soon enough, will reduce the pressure in the eye. By careful monitoring, a dog can be maintained (at the veterinary centre) until an operation is undertaken. This can be a period of some days or even weeks. Alternatively, some surgeons allow dogs to go home with the owner administering the pressure reducing treatment, until the lens has become almost completely detached and moved to a suitable position so that it can be easily removed.
The lens is also attached to the vitreous humour (the jelly like substance) in the eyeball itself. In order to remove the lens, it has to be severed from the vitreous humour. This is a delicate operation, as it is possible that any outward pressure on the lens can move the whole of the vitreous humour forward which can detach the retina with consequent loss of vision. Some vitreous humour is inevitably removed with the lens, though in a successful operation the surgeon takes as little as possible because the space left by the lens and removed vitreous humour causes an imbalance within the eye. In this situation, there is a tendency for the vitreous humour to move forward causing partial or complete retinal detachment. Some surgeons remove the lens prematurely by forcible suction, the majority hold that this is not advisable that because of the danger of retinal detachment by this method. In addition, there is usually more chance of haemorrhage (internal bleeding), more scar tissue, again increasing the likelihood of retinal detachment.
Because stability of the eye has been upset, surgeons recommend that the dog does nothing that might cause the movement of the retina. For instance ‘rat killing’ (violent toy shaking). Even straining against a collar is considered by some to be inadvisable, so they recommend a body harness (which does not bear on the neck).
After successful treatment, the eye has no focusing ability and the light image which would (at least in humans) be inverted by the lens now falls directly on the retina. However, in dogs, apparently, the cornea (the structure in front of the lens) provides an appreciable focusing (though fixed) element to the eye and although focusing is absent, some resolution of an image should be possible. Presumably, in time, the brain will eventually learn to interpret what falls on the retina, which should give the dog the so called ‘guidance vision’.
Sometimes, the short term results are good, particularly if both eyes have retained their retinas. However, as mentioned, prolonged glaucoma may have already caused irreparable damage to the retina. In addition, this major alteration to the structure of the eye can lead to glaucoma again! The eventual consequences of glaucoma require removal of the eye.
Aftercare:
Surgeons recommend that the dog should generally be kept quite for a number of days and stress the importance of the regular and continued use of the eye drops supplied.
At least one specialist recommends that the dog be seen at intervals of several months to check that the IOP has not risen to dangerous levels.
One ophthalmic surgeon states that further surgery is essential to maintain vision. He recommends laser treatment to reduce to capability of the eye to produce aqueous humour. In human eye conditions where the retina is detaching from the eye, lasers can be used to pin the retina back against the eye.
Advice:
Be prepared. A normal vet will NOT be able to carry out this treatment, so he will refer you to a specialist.
Is there one within a reasonable distance of you, which has suitably qualified staff for this operation?
Do these staff maintain a 24 hour rota and will they see a luxated dog immediately and at ANY time/day?
Do you have their telephone number?
Does the phone number you have been given actually work at any time? Why not try it some bank holiday?
If you think your dog is at risk, find a centre that is prepared to take action, when necessary, quickly.
Keep looking at your dog and notice any particular change in behaviour that might be eye related.
Other Stuff:
In
It is possible to insert (permanently) which is called a shunt, a small valve, into the eye which can relieve excess pressure, though this tube can sometimes become blocked.
If glaucoma necessitates removal of the eye (enucleation), this is usually a straightforward operation with no complications. It is possible to insert a silicone implant within the eye after removing the contents (called evisceration). This apparently results in a normal looking pain free eye, but with no vision of course.
Maybe you think all vets should have a tonopen? They could then be in a position to administer the pressure reducing drugs, however, the cost of one of these instruments approaches £2,000.