Massive muscle myositis
The masticatory muscle myositis ( Syn. Myositis eosinophilica , Atrophic myositis , masticatory muscle myositis ) is an uncommon in domestic dogs occurring autoimmune disease caused by an inflammation of the muscles of mastication is characterized. The disease leads to disturbances in the mobility of the lower jaw and thus to hindrance to the intake of food and fluids. With timely treatment, the chances of recovery are good, with the chronic form, however, questionable.
Occurrence and pathogenesis
Masticatory muscle myositis occurs in dogs of all breeds and ages. An accumulation is described for the German Shepherd Dog , the Doberman and all Retriever breeds . Young and middle-aged animals tend to get sick. There does not seem to be any gender predisposition.
The limitation of the disease to the masticatory muscles is due to their special origin from the first gill arch . The chewing muscles are characterized by a special type of muscle fiber , the so-called 2M muscle fibers , which have a special isoform of myosin . The main antigen involved is called masticatory myosin binding protein-C . The organism produces IgG antibodies against this for reasons that have not yet been clarified . In the course of an antigen-antibody reaction , inflammation occurs with immigration of various immune cells ( macrophages , lymphocytes and plasma cells ) and finally death ( necrosis ) and the breakdown of muscle cells. According to the latest studies, the disease could also be a T-cell- dependent immune disease, which leads to muscle fiber destruction and thus to the production of autoantibodies against the myosin, because no autoantibodies can be detected in a third of the animals affected despite cell damage. According to the VETAMIN-D scheme , the disease is caused by inflammation. In the further course, the destroyed muscle tissue is replaced by connective tissue .
The acute masticatory muscle myositis is characterized by a swelling on both sides of the masticatory muscles side of the head. The region is often painful. The affected animal mostly shows a reduced food and fluid intake. Occasionally, fever is observed; enlargement of the mandibular lymph nodes and tonsils also occurs in some cases. Blood tests may show a slight increase in creatine kinase activity and occasionally eosinophilia (hence the outdated name myositis eosinophilica ).
The more common chronic masticatory muscle myositis is characterized by shrinkage ( atrophy ) of the masticatory muscles, which makes the head look narrow ("fox-skulled") in the posterior area. Through the connective tissue replacement of the musculature, the lower jaw becomes increasingly, both actively and passively, only limited in its mobility. This can lead to a blockage of the mouth (pseudo- trism ). In some cases, the eyeballs recede deep into the eye sockets as a result of the loss of muscle mass. Chronic masticatory muscle myositis can develop from the acute form or occur independently.
The clinical suspected diagnosis can be supported by an electromyogram (EMG), in which changes are found exclusively in the masticatory muscles. A biopsy with subsequent histological evidence of fiber damage or evidence of autoantibodies are considered to be evidence of the presence of the disease.
Polymyositis and diseases of the temporomandibular joint must be excluded from the differential diagnosis . In chronic disease also needs a nerval of related atrophy caused by damage to the mandibular nerve are thought as in the much rarer idiopathic trigeminal - neuritis occurs. Masticatory muscle atrophy can also occur as a result of long-term treatment with glucocorticoids , which must be taken into account when taking the medical history , or in the case of leishmaniasis .
The acute form is treated by administering glucocorticoids , possibly in combination with azathioprine . These active ingredients dampen the immune system (so-called immunosuppressants ) and thus the pathological reaction in the muscle tissue. The duration of treatment depends on the success of the treatment and possible recurrences and can be up to six months. In the chronic form, repeated stretching of the masticatory muscles can be attempted under anesthesia ; However, this method is controversial because, in the opinion of the opponents of this method, an existing inflammation can be intensified and there is a risk of dislocations and fractures of the lower jaw. Also, physiotherapy and animating to active chewing (Kauknochen) can be tried.
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