by Cindy Atwood, DVM, May 2008
A polyneuropathy is a disease that affects more than one nerve. There are many different forms of polyneuropathy and many different causes including toxic, metabolic (chronic liver disease) and endocrine (diabetes, hypoglycemia, hypothyroidism, etc.) immune-mediated, carcinomatous, idiopathic and inherited. The Leonberger can suffer from any of these forms of polyneuropathy. Leonberger Polyneuropathy (LPN) refers to the heritable form. LPN affects the longest (peripheral) nerves of the body. This causes weakness and dysfunction in the muscles which are innervated by these nerves. LPN is progressive and often debilitating; if the larynx is involved it can be fatal.
Symptoms: The most common early symptoms of LPN are gait abnormalities and/or a weakness in the rear limbs. As these are non-specific symptoms, it is frequently confused with other problems. Often subtle, it may show simply as a shortened stride on one side or a slight dragging/wearing of the toenails. Progression may be slow and gradual or rapid. Lack of feeling and weakness is secondary to nerve degeneration and may present as misplacement of the feet and stumbling, wobbling, crossing of the limbs exaggerated and lengthened stride or sometimes a high stepping “marrionette-like” walk. Though these signs usually involve the rear limbs, they may also occur in the forelimbs. If the recurrent laryngeal nerve is affected, there may also be a change in bark, wheezing, heavy loud panting, and difficulty breathing especially with exercise, and coughing or choking with eating or drinking. Over the past few years, we have diagnosed dogs with symptoms ranging from very mild to very severe. The signs became apparent as early as a few months of age to as late as over 8 years of age.
Diagnosis: If LPN is suspected, a veterinary neurologist should be consulted. Careful physical, orthopedic, and neurological examinations are the place to start. Routine blood work and radiographs should help rule out other causes of lameness and polyneuropathy. We would strongly encourage you to seek an expert opinion after consultation with your regular veterinarian as, sadly, this disease is as yet not well known and has often been misdiagnosed as something else. More advanced tests, including nerve conduction velocity and muscle and nerve biopsies are needed to make a definitive diagnosis.
Treatment: As of this time, there is no curative treatment for this disease though there are several nutritional supplements that have been recommended which may help to delay the progression of symptoms and appeared to have offered some improvement in others.
We continue to find an increasing number of affected dogs worldwide. There are a number of people working very hard on this issue including breeders, veterinarians, and researchers at several different facilities. The focus is on determining the mode of inheritance by pedigree analysis (extremely difficult when there are many dogs we do not know were/are affected) and by looking for the genetic markers or actual causative gene(s) in order to develop a blood test for carriers. We are also trying to collaborate with researchers in Europe.
If you suspect you have a dog affected by this disease please contact your LCA Health Committee (HREC) LPN representative who can give you further information or help you to find a veterinary neurologist in your area.
Pre or Post-Mortem Biopsies:
Dr Ned Patterson and Dr. Mickelson at the University of Minnesota are conducting an on-going research study in the hopes of finding the causative gene(s) and a developing a DNA test that will identify ILP carriers and affected dogs. This is of utmost importance to the Leonberger breed in general and specifically for all Leonberger breeders internationally. To further their efforts it is critical that biopsies be performed on all affected dogs as well as immediate relatives of affected dogs.
Dr. Diane Shelton is a neuropathologist who reads these biopsies. She requires the following from your veterinarian:
A biopsy of the cranial tibial muscle and of the the peroneal nerve. Ideally samples both in 10% formalin and fresh chilled samples..
Please send these to:
Department of Pathology
University of California, San Diego
La Jolla, CA 92093-0612