What is the other terminology for neuromuscular diseases?
generalized lower motor neuron diseases
What are the general findings in neuromuscular diseases?
-decreased ability to bear weight
-decreased muscle tone and mass
-possible decreased spinal reflexes
What are the general clinical signs of myopathies?
-weakness
-crouched stance
-stiff, short-strided gait
-tremors
-possible myalgia (muscle pain)
-possible abnormal muscle size
-normal postural reactions and spinal reflexes
Why do myopathy patients often present with hypertrophy first, followed by atrophy?
-hypertrophy occurs from inflammation/swelling of muscles
-atrophy occurs once disease process starts to break down the muscles
Why is it important to support a suspected myopathy patient’s weight when testing postural reactions and spinal reflexes?
a lack of appropriate postural reaction/spinal reaction due to weakness could be mistaken for neuronal disease
How does the rate of atrophy differ with nerve vs muscle disease?
-atrophy with nerve diseases is rapid
-atrophy with muscle diseases is gradual
What is autoimmune polymyositis?
diffuse immune-mediated disease directed against skeletal muscle
What are potential triggers for autoimmune polymyositis?
-often idiopathic
-systemic lupus erythematosus
-paraneoplastic syndrome (round cell tumors in boxers)
-trimethoprim-sulfa use in dobermans
What are the clinical signs of autoimmune polymyositis?
-large breed dogs
-generalized weakness that worsens with exercise
-muscle swelling/hypertrophy followed by atrophy
-megaesophagus
-possible myalgia/shifting leg lameness
-possible signs of systemic illness
How is autoimmune polymyositis diagnosed?
-elevated CK and AST
-muscle biopsy
-rule out infectious causes
What is the treatment for autoimmune polymyositis?
-immunosuppression, starting with glucocorticoids
-months of treatment with a months-long taper
What are the characteristics of masticatory muscle myositis?
-focal immune-mediated disease
-directed against muscles of mastication
What are the clinical signs of masticatory muscle myositis?
-large breed dogs
-bilateral signs
-muscle swelling (acute)
-pain on palpation (acute)
-symmetric muscle atrophy with trismus/lockjaw (chronic)
What is the treatment for masticatory muscle myositis?
immunosuppression with prednisone +/- adjunctive immunosuppressives
Why is it important to NOT force the mouth open in MMM patients with trismus?
-exacerbates restrictive fibrosis
-can break the jaw
What is the prognosis for masticatory muscle myositis?
-good if treated early and aggressively
-some atrophy may persist
What are the most common causes of infectious myositis?
protozoa
-neospora
-toxoplasma
What is the biggest differential/rule out for infectious myositis?
meningitis
What are the clinical signs of infectious myositis?
-often non-specific
-possible systemic signs
-CNS and PNS effects
-young or immunocompromised animals
How is infectious myositis diagnosed?
-possible increased CK
-serology or PCR with serology sample or biopsy
What is the treatment for protozoal infectious myositis?
clindamycin, TMS, or ponazuril
Which metabolic diseases can cause hypokalemic myopathy?
-kidney disease
-hyperthyroidism
How is hypokalemic myopathy diagnosed?
-serum K+ less than 3.0 mEq/L
-CK moderately elevated
What is the treatment for hypokalemic myopathy?
-potassium supplementation
-address underlying disease
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