Introduction
This is an emerging
inherited disease in the Leonberger and has only recently been recognised
in the UK.
The condition was first diagnosed in the USA some 5 years ago in
Ohio.
Polyneuropathy is a
condition which affects the nerves and in this condition the nerves
furthest away from the spine tend to be affected first, but the condition
is progressive and more nerves become affected with time. There appears
to be a loss of structure of the nerves and a loss of nerve fibres within
the larger nerves. The condition is very similar to an inherited human
condition Charcot-Marie-Tooth Disease. Recent research by Dr Diane
Shelton at the University of
California,
San Diego has shown that
the condition is inherited in the Leonberger.
The mode of inheritance is
X linked and recessive with partial penetrance. In the study published
(Shelton GD, Podell M, and others: Inherited polyneuropathy in Leonberger
dogs: a mixed or intermediate form of Charcot-Marie-Tooth disease? Muscle
Nerve. 2003 Apr; 27(4):471-7) 40% of males were affected (with full
penetrance 50% of males would be affected). It has been diagnosed in a
female Leonberger. Further work needs to be carried out in order to fully
determine the mode of inheritance. Dr Shelton hopes that her research
will not only act as a model for Charcot-Marie-Tooth Disease, but will
also help to identify the gene(s) responsible for this terrible condition
in the Leonberger.
What signs to look for?
The onset of this
condition is slow and can be easily missed until the clinical signs are
severe.
Typically, young male dogs
are most likely to be presented with this disease. Exercise intolerance or
reduced exercise tolerance may be one of the first signs seen. Later the
dog may develop a change in the pitch of his bark; it becomes deeper and
more hoarse.
The most obvious clinical
sign is a very noisy breathing associated with the throat. In the
beginning this is most noticeable as the dog breathes in. The noise is
termed ‘stridor’ and is a hoarse rasping sound. This noise together with
the change in bark is due to the effect on the nerve to the larynx (voice
box). The failure of the main cartilages of the larynx to move sideways
(laryngeal
paralysis) when the dog breathes in leads to vibration and the noise.
Regrettably as the disease progresses this reduces the amount of air which
flows into the lungs and will lead to severe exercise intolerance, great
difficulty in breathing, the development of a bluish (cyanosis) tinge to
the mucous membranes and may lead to collapse.
The breathing is usually
worse in hot weather as they find it difficult to pant and therefore do
not lose heat effectively.
The affected dogs also
develop a high stepping gait to the hind limbs, typically it is a
‘bicycle’ like action. This occurs due to nerves in the lower hind legs
not sending signals effectively to the muscles
As the disease progresses
the gait gets worse and more and more uncoordinated. Eventually, as the
nerves die back, the muscles will waste away and be inactive, this can
then lead to paraplegia (loss of use of the hind legs) and to tetraplegia
(loss of use of all four legs).
Confirming the
Diagnosis
This may need to be
carried out by a specialist in neurology. The Royal College of Veterinary
Surgeons has a list of UK specialists.
A tentative diagnosis can
be made based on breed, age and sex together with the symptoms of
laryngeal paralysis. Laryngeal paralysis is a diagnosis which can be
confirmed by giving the dog a very light general anaesthetic and looking
for movement of the cartilages of the larynx.
Definitive diagnosis can
be made by biopsy of the cranial tibial muscle and the peroneal nerve.
The cranial tibial muscle is on the front aspect of the shin immediately
below the stifle joint which makes it a very accessible biopsy site. The
peroneal nerve runs to the lower hindleg – such a biopsy should only be
carried out by those familiar with the technique of nerve biopsy. The
samples need to be sent to Dr Shelton’s laboratory in California.
Can we treat this
condition?
Unfortunately as for the
human form of the disease and other progressive nerve diseases such as
Multiple Sclerosis there is currently no treatment. It may however be
possible to help reduce the severity of the disease in its early stages.
Laryngeal paralysis,
though not curable, can be managed surgically. Surgery aims to widen the
opening of the larynx so that air flow is improved. Most surgeons will
operate only on the left side as there is a risk, if both sides are
operated on, that food and liquid could enter the airway and lead to
pneumonia.
The surgery has a success
rate of around 85% and involves moving one cartilage sideways and fixing
it in a permanently open position. There are risks associated with this
surgery and it should only be carried out by surgeons who are competent in
the technique.
By carrying out this
surgery, the dog’s breathing should become easier, though it will always
be noisier than in the normal dog. This should, at least in the short
term, improve the dog’s quality of life.
The future
Unfortunately we cannot
stop the disease progressing and affected dogs will need a lot of tender
loving care until their quality of life deteriorates. It is for breeders,
owners and vets to help identify this devastating disease, to identify its
mode of inheritance and hopefully to be able to eradicate it before it
becomes widespread in the Leonberger community. It is now recognised in
the USA,
UK and
mainland Europe
Further
Information/Bibliography
Detailed information is
available at:
http://medicine.ucsd.edu/vet_neuromuscular/cases/1999/aug99.html
http://www.leowatch.org/HTMLfiles/Health
issues/polyneuropathy.htm
Shelton GD, Podell M, and
others: Inherited polyneuropathy in Leonberger dogs: a mixed or
intermediate form of Charcot-Marie-Tooth disease? Muscle Nerve. 2003 Apr;
27(4):471-7
The author is a
veterinary surgeon who qualified in 1984, and his career has included
being in general practice, a university residency (surgery training
program) and 6 years as a university lecturer in small animal surgery. He
is a European specialist in small animal surgery and currently works in a
private referral surgical practice in Cheshire.
