It is assumed to be an autoimmune disease that causes chronic inflammation of one or more muscle groups resulting in loss of functionality and muscle weakness in the affected areas. Myositis is a progressive form of the disease with a very poor prognosis. We see two groups. The first group consists of relatively young dogs with swallowing or eating problems. The second group consists of dogs that are young to middle aged and have more musculoskeletal problems and sometimes a combination with swallowing problems. Depending on the location , the most common symptoms are:
• reduced endurance
• muscle weakness
• swallowing problems
• fever
• general fatigue
• lack of drive to play or walk
• lameness
• stiffness
• walking with curved back
• salivation
• vomiting
• poor appetite
Because many symptoms are also features of other disorders, this condition is often difficult to recognize. If left undiagnosed, myositis is lethal; if diagnosed early, available treatments are immunosuppression and management with steroids. Kooikers with myositis seem to pass away at 3 or 4 years after being diagnosed. Myositis in general can be hereditary or caused by infections, autoimmune diseases and toxins. It can be misdiagnosed as Myasthenia Gravis, for example, by veterinarians. In order to make a definitive diagnosis, a muscle biopsy by a qualified veterinarian is required. This tricky disease has been found more often in the Kooikerhondje population in recent years. We hope that current research in the Netherlands will give us a better understanding of the disease in the near future. There is no gender disposition which means males and females are affected equally. It is difficult for general veterinarians that are not specialized to make the diagnosis.
The medical work-up includes an electro-myography (test to measure the muscle reaction after a stimulus is given) and a muscle biopsy (tissue sample taken from the affected muscle group). If the dog has difficulty swallowing, a bronchoscopy (internal exam with a camera visualizing the lungs and bronchial tree) as well. Before starting steroid therapy, the diagnosis of Polymyositis needs to be confirmed because steroids can alter test results. Dr. Paul J.J. Mandigers from the Veterinary Faculty at Utrecht University in The Netherlands thinks that Polymyositis in the Kooiker is a breed specific disease that is familial and hereditary. There is most likely a trigger that causes Polymyositis to break out. Dr. Mandigers is the leading world expert on PM. If your kooiker has been definitively diagnosed with PM, please contact him at p.j.j.mandigers@veterinair-neuroloog.nl (p.j.j.mandigers@veterinair-neuroloog.nl)to report your case and get the most up to date information on course of treatment for the disease. New developments in treatment are being made everyday.
Dr. Mandigers and Utrecht University have developed a partial genetic test for Polymyositis that can give a general risk assessment. This blood test can be run in conjunction with the DNA test for ENM and vWD, and detects the presence of 2 identifiable markers for PM. Dogs are given the designation of clear (WW - homozygous wildtype), carrier (WM - heterozygous), or affected (MM). Please note that any of the designations do not mean that your dog will or will not develop PM, they simply give an idea of the risk of your kooiker developing the disease.
Frequency
Unfortunately we see polymyositis more regularly at the moment. The frequency is around 1% of the population.
How to Test for PM
4 ml of blood in an EDTA tube or a cheek swab sent to the University of Utrecht. Download the DNA test form at the top of this page for you and your veterinarian to fill out and send to the university in The Netherlands. ENM, vWD, and PM can be combined on one form and blood sample/cheek swab.