[pyrnet] Myositis

["Linda Weisser" <lmweisser@attbi.com>]

If you search google for "masticatory myositis canine" you will find many,
many references.  I'm going to send just a couple

Linda


http://www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00068.htm
IMMUNE MEDIATED MUSCLE DISEASES

Canine polymyositis is usually seen in large breed dogs (incidence in
females is greater than males). It is an acute disease causing progressive
weakness of the head, trunk, and limbs. The clinical signs include pain,
undulating fever, dysphagia, and megaesophagus. Diagnosis is by eosinophilia
on the CBC, leukocytosis, increases in ALT, LDH, and CPK. Fifty percent of
cases will have immunofluorescence for ANA or antisarcolemmal
antibodies.(15) Biopsies demonstrate Type I and II fibres with multifocal
necrosis with vacuolization and hyalinization. Treatment is with
corticosteroid at 0.5 mg-1 mg/kg q12h. If a response is noted after one
week, the prognosis is good.(15)

Masticatory myositis involves antibodies directed at the type 2M fibres
unique to the muscles of mastication: the temporalis, masseter and
pterygoid. Embryologically these muscles are derived from mesoderm.(16) By
two weeks postpartum, these muscles have developed the unique 2M fibres.

There are two distinct disorders in masticatory myositis: 1) acute
eosinophilic myositis; and 2) chronic atrophic myositis.

Eosinophilic myositis is prevalent in German Shepherds and Dobermans of a
young age (less than four years). The acute phase lasts two to three weeks
followed by remission and recurrent attacks. Peripheral eosinophilia is
noted. Histology reveals large numbers of eosinophils, plasma cells
infiltrating the muscles, hemorrhage, and necrosis. Chronic lesions
demonstrate scar tissue. Treatment involves use of corticosteroids at 0.5-1
mg/kg.(17)

Atrophic myositis has no breed, sex, or age predilection. There is usually a
single less dramatic attack followed by progressive atrophy and fibrosis.
Peripheral eosinophilia is not a feature. Eosinophils are less predominant
in histology. Treatment is less effective and the prognosis is guarded.(17)

Masticatory myositis has been described as a result of infection with the
protozoa Leishmania infantum.(18) Leishmania is transmitted by the sandfly
and is zoonotic. The disease is endemic in the Mediterranean and Portugal
with sporadic reports in Europe and the United Kingdom. Muscle fibre
necrosis, atrophy, mononuclear infiltrates, vasculitis, and amastigotes
within macrophages are histological features. IgG immune complexes have been
detected.(18)