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320 Facial Muscle Wasting

Facial Muscle Wasting Client Education
Sheet
VetBooks.ir Advanced or Confirmatory Testing

Weakness (decreased jaw tone) or
BASIC INFORMATION
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masticatory muscle fibrosis (increased • Muscle biopsies and histopathology:
Definition jaw tone or trismus [inability to open ○ Immunohistochemistry shows lack of
Atrophy of the muscles of mastication, primarily the mouth]) dystrophin (MD).
temporal and masseter muscles ■ Painful mastication and crying while ○ High proportion of centralized myofiber
chewing: MM, TMJ dysplasia nuclei (CM)
Synonym ○ Generalized ○ Antibodies against type 2 myofibers on
Masticatory muscle atrophy ■ Concomitant mild to severe weakness, frozen sections of muscle (MM)
exacerbated by exercise; generalized ○ Myofiber necrosis with mononuclear cell
Epidemiology muscle atrophy infiltrates, atrophy, and fibrosis (DM)
SPECIES, AGE, SEX ■ Bunny hopping gait progressing to a more ○ Multifocal necrosis and phagocytosis of
Dogs (most commonly) and cats (rarely), any stilted gait with a plantigrade stance: MD type 1 and type 2 myofibers (IP)
age, any sex; with muscular dystrophy (MD), • Circulating serum antibodies against type 2
only males affected PHYSICAL EXAM FINDINGS myofiber muscle fibers: MM
• Full physical exam, paying particular atten- • Serologic titers for Toxoplasma and Neospora:
GENETICS, BREED PREDISPOSITION tion to the head, condition of other muscle protozoal myositis
• German shepherds, retrievers, Doberman groups, and skin • DNA-based tests are available for some
pinschers, spaniels: masticatory myositis • Bilateral atrophy of the temporal and masseter neuromuscular diseases: DM, CM
(MM [p. 637]) muscles; skull-like appearance of the head • Electromyography is more useful in deter-
• Shetland sheepdogs, rough- and smooth- ○ Dogs with MM can show salivation, mining neurologic rather than muscular cause
coated collies: dermatomyositis (DM) dysphagia, and difficulty in opening the of the atrophy.
• German shepherds, other large breeds: mouth, progressing to trismus.
idiopathic polymyositis (IP) ○ Dogs with DM can show generalized TREATMENT
• Large-breed dogs: glucocorticoid-induced muscle atrophy, skin lesions, decreased
muscle atrophy jaw tone, facial nerve paralysis, stiff gait, Treatment Overview
• Congenital myopathies dysphagia, and regurgitation. • Treatment depends on the underlying cause
○ Labrador retrievers: centronuclear • Enophthalmos, with third eyelid protrusion and may include glucocorticoid therapy to
myopathy (CM) and X-linked myotubular and small palpebral fissure due to dramatic halt the process of muscle inflammation
myopathy loss of retrobulbar muscular support (p. 716) or appropriate antibiotics or antiprotozoal
• MDs • Unilateral temporal muscle atrophy: ipsilat- therapy for infectious myositis.
○ Golden retrievers, Labrador retrievers, eral denervation of the mandibular branch • Glucocorticoid therapy
German short-haired pointer, and of the trigeminal nerve ○ Masticatory myositis (p. 637)
Cavalier King Charles spaniels: dystrophin ○ Idiopathic polymyositis: prednisone
mutations Etiology and Pathophysiology 1-2 mg/kg PO q 12h × 14 days, then
○ Boston terriers, cocker spaniels, and • Developmental tapering over at least 4 weeks to 12
Chihuahuas: sarcoglycan deficiency • Neuropathy months or longer
○ Brittany spaniel, springer and spaniel • Infectious ○ DM (varied response)
mixed-breed dog, and cats: laminin • Immune mediated • Upright feeding of dogs with megaesophagus
alpha-2 deficiency • Iatrogenic
○ Sphinx and Devon rex cats: alpha- • Metabolic Possible Complications
dystroglycan deficiency • Neoplastic Glucocorticoid side effects
• Bassett hounds: temporomandibular joint • Disuse atrophy
(TMJ) dysplasia Recommended Monitoring
DIAGNOSIS Monitor for glucocorticoid side effects, and
ASSOCIATED DISORDERS taper the dose, depending on muscle condition
• Submandibular and prescapular lymph- Diagnostic Overview and function.
adenopathy (p. 598) Specific diagnosis is often made histopatho-
• Generalized muscle atrophy logically, with the exception of serologic titers PROGNOSIS & OUTCOME
for infectious causes or for the detection of
Clinical Presentation antibodies against type 2M muscle fibers. Varies, depending on the underlying cause;
HISTORY, CHIEF COMPLAINT process is reversible provided no extensive
• Detailed history, including previous bouts of Differential Diagnosis fibrosis
painful mastication or chronic glucocorticoid See Etiology above and a complete differential
use list (p. 1222). PEARLS & CONSIDERATIONS
○ Chronic daily glucocorticoid administra-
tion may cause facial muscle wasting. Initial Database Comments
• History may reflect abnormalities isolated to • CBC usually normal by the time the muscles • Facial muscle atrophy is a common feature
facial musculature or generalized myopathy. are atrophied of many emaciating conditions in which
○ Facial • Serum biochemistry profile there is also generalized loss of lean body
Prominence of external occipital ○ Elevated muscle enzyme levels (creatine mass.
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protuberance kinase and aspartate aminotransferase): IP, • Generalized muscle atrophy is often first
Difficulty or inability to prehend food MM, DM, MD, CM noticed in the facial muscles, especially in
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(less common) ○ Hyperglobulinemia: IP long-haired breeds.
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