Difference between revisions of "Masticatory Muscle Myositis"

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==Overview==
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(MMM)
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:
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*Occurs in dogs
*'''Acute stage''': Eosinophilic myositis with extremely swollen, painful, hard masticatory muscles.
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*Tends to affect the masseter and temporalis muscles
*'''Chronic stage''': Atrophic myositis where atrophy may occur without previous acute stage.
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*Autoantibodies selectively attack muscles of mastication (type IIM fibres)
 
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*Acute stage = eosinophilic myositis
Grossly MMM is normally bilateral, but not necessarily symmetrical.
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**Extremely swollen, painful, hard masticatory muscles
 
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*Chronic stage = atrophic myositis
==Histology==
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**Atrophy may occur without previous acute stage
 
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*Grossly:
'''Acute lesions''':  
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**Bilateral but not necessarily symmetrical
*Mainly eosinophilic infiltrate, few lymphocytes, [[Monocytes|monocytes]] and plasma cells.
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**At first, enlarged and oedematous muscles becominf dark red, firm with reddish streaks and yellowiss foci
*In recurrent disease plasma cells predominate.
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*Histologically:
*[[Muscle Necrosis|Necrotic]] myofibres, [[Muscle Atrophy|atrophy]] and attempted [[Muscle Regeneration|regeneration]].
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**Acute lesions:
 
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***Mainly eosinophilic infiltrate, few lymphocytes, [[Monocytes|monocytes]] and plasma cells
'''Chronic lesions''':
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***In recurrent disease plasma cells predominate
*[[Muscle Atrophy|Atrophy]] predominates.
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***[[Muscle Necrosis|Necrotic]] myofibres, [[Muscle Atrophy|atrophy]] and attempted [[Muscle Regeneration|regeneration]]
*Fasciculi are shrunken.
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**Chronic stage:
*Condensation of stroma leading to an enlarged endomysium.
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***[[Muscle Atrophy|Atrophy]] predominates
*Focal plasma cell and lymphocyte infiltration.
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***Fasciculi are shrunken
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***Condensation of stroma -> enlarged endomysium
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***Focal plasma cell and lymphocyte infiltration
  
  
 
[[Category:Immune-Mediated Myositis]]
 
[[Category:Immune-Mediated Myositis]]
 
[[Category:To Do - Musculoskeletal]]
 
[[Category:To Do - Musculoskeletal]]
[[Category:Other Oral Conditions]]
 

Revision as of 13:31, 20 June 2011

(MMM)

  • Occurs in dogs
  • Tends to affect the masseter and temporalis muscles
  • Autoantibodies selectively attack muscles of mastication (type IIM fibres)
  • Acute stage = eosinophilic myositis
    • Extremely swollen, painful, hard masticatory muscles
  • Chronic stage = atrophic myositis
    • Atrophy may occur without previous acute stage
  • Grossly:
    • Bilateral but not necessarily symmetrical
    • At first, enlarged and oedematous muscles becominf dark red, firm with reddish streaks and yellowiss foci
  • Histologically:
    • Acute lesions:
    • Chronic stage:
      • Atrophy predominates
      • Fasciculi are shrunken
      • Condensation of stroma -> enlarged endomysium
      • Focal plasma cell and lymphocyte infiltration