Changes

(MMM)

*Occurs in dogs

Masticatory muscle myositis (MMM) occurs in dogs and tends to affect the [[Mastication#Jaw Closing Muscles|masseter]] and [[Cheeks|temporalis]] muscles. Autoantibodies selectively attack the muscle of mastication, which contain type IIM fibres. MMM can be classified as either acute or chronic:

*Tends to affect the masseter and temporalis muscles

*'''Acute stage''': Eosinophilic myositis with extremely swollen, painful, hard masticatory muscles.

*Autoantibodies selectively attack muscles of mastication (type IIM fibres)

*'''Chronic stage''': Atrophic myositis where atrophy may occur without previous acute stage.

*Acute stage = eosinophilic myositis

 

**Extremely swollen, painful, hard masticatory muscles

Grossly MMM is normally bilateral, but not necessarily symmetrical.

*Chronic stage = atrophic myositis

 

**Atrophy may occur without previous acute stage

*Grossly:

 

**Bilateral but not necessarily symmetrical

'''Acute lesions''':  

*Mainly eosinophilic infiltrate, few lymphocytes, [[Monocytes|monocytes]] and plasma cells.

**Acute lesions:

*In recurrent disease plasma cells predominate.

***Mainly eosinophilic infiltrate, few lymphocytes, [[Monocytes|monocytes]] and plasma cells

*[[Muscle Necrosis|Necrotic]] myofibres, [[Muscle Atrophy|atrophy]] and attempted [[Muscle Regeneration|regeneration]].

***In recurrent disease plasma cells predominate

 

***[[Muscle Necrosis|Necrotic]] myofibres, [[Muscle Atrophy|atrophy]] and attempted [[Muscle Regeneration|regeneration]]

'''Chronic lesions''':

**Chronic stage:

*[[Muscle Atrophy|Atrophy]] predominates.

***[[Muscle Atrophy|Atrophy]] predominates

*Fasciculi are shrunken.

***Fasciculi are shrunken

*Condensation of stroma leading to an enlarged endomysium.

***Condensation of stroma -> enlarged endomysium

*Focal plasma cell and lymphocyte infiltration.

***Focal plasma cell and lymphocyte infiltration

[[Category:Immune-Mediated Myositis]]

[[Category:Immune-Mediated Myositis]]

[[Category:To Do - Musculoskeletal]]

[[Category:To Do - Musculoskeletal]]

[[Category:LisaM reviewing]]

[[Category:Other Oral Conditions]]