1. POLYMYOSITIS
Emily Jones

2. Bracken, Shaw
 11y 10m English Springer
Spaniel
 Male Neutered
 Fully vaccinated
 Dewormed
 Presenting with a 5 week
history of:
› Paraparesis
› Lethargy
› Decreased appetite

3. Clinical Exam
 Weakness seen in all limbs, especially the
hind limbs
 Able to move all four limbs
 No neurological deficits
 Non painful
 TPR within normal limits

4. Differential Diagnosis
 Immune Mediated Polymyositis
 Paraneoplastic polymyositis
 Chronic degenerative radiculomyelopathy
 Toxoplasma gondii
 Neospora caninum
 NEOPLASIA:
 Bronchogenic carcinoma
 Myeloid leukemia
 Tonsillar carcinoma
 Lymphoma
 Muscular dystrophy
 Idiopathic polyradiculoneuritis
 Rickettsial polymyositis
 Myasthenia gravis

5. Polymyositis
 The most frequently seen non-traumatic
muscle disease
 Middle aged, large breed dogs
 Generally assumed to be an immune-
mediated disease of skeletal muscle
› Can occur in association with Systemic Lupus
Erythematosus
 May be associated with neoplasia
 Lymphoma
 Thymoma
 Bronchogenic carcinoma

6. Clinical Signs
 Weakness
 Lameness
 Reluctance to exercise
 Weight loss
 Muscle atrophy
 Stiff gait
 Muscle pain on palpation
 Regurgitation caused
by megaoesophagus
 Dysphagia
 Excessive salivation
 Weak bark
 Pyrexia
 Tongue dysfunction

7. Diagnosis
 Muscle Biopsies
 Mixed mononuclear cell
infiltration
 Generalised atrophy
 Creatine Kinase
 Elevated in myopathies
 Electromyography
 Increased electrical
activity produced by
skeletal muscles.

8. Features required for a
diagnosis of Immune
Mediated Polymyositis?
1. Clinical signs of weakness
2. Elevated Creatinine Kinase
3. Abnormal Electromyography
4. Absence of an underlying cause
5. A muscle biopsy which shows an
inflammatory infiltrate

9. Approach to Bracken’s Case
 Haematology: unremarkable
 Biochemistry
› Elevated Creatine Kinase 4042 u/L (52-368)
› Elevated AST 230 u/L (13-15)
› Elevated ALT 218 u/L (10-109)
 Abdominal Ultrasound
› Small mass found in the dorsal wall of the
bladder (20x10mm)
› Slightly R enlarged medial iliac LN (7.5mm)

10.  Chest Radiographs
› Moderate shoulder DJD
 Cardiac Ultrasound
 Neospora and Toxoplasma
› Negative for neospora
 Electromyography
› Abnormal spontaneous electrical activity
recorded in the skeletal muscles
 CSF Tap
› 800 protein – normal?

11. Biopsy Report
 Mild to marked, perivascular to
interstitial lymphocytic infiltrate
 Lymphocytes invade into
degenerate or necrotic myofibers .
 Up to 20% of the myofibers have
some degree of degeneration or
necrosis
› swollen, fragmented
 Multifocal, mild, interstitial fibrosis,
often associated with areas of
inflammation.
 Triceps biopsy least affected with less
inflammation and fewer degenerate
and necrotic fibers.

13. Treatment
 Immunosuppression
› Prednisolone
› Azathioprine
› Cyclosporin
› Cytarabine
 Analgesia
› Buprenorphine
 Antibiotics
› Amoxicillin/Clavulanic Acid
› Clindamycin

14. Prognosis

15. Bracken’s Progress?
 Slowly improving
 Receiving physiotherapy every day

16. References
 http://vetneuro.com/Portals/124/Forms/Evans%20Myopthies.
pdf
 http://vetbook.org/wiki/dog/index.php/Polymyositis
 http://vetneuromuscular.ucsd.edu/cases/2006/july06.html
 http://www.merckmanuals.com/vet/appendixes/reference_
guides/serum_biochemical_reference_ranges.html
 http://www.ed.ac.uk/polopoly_fs/1.98000!/fileManager/Case
_study_06.pdf
 http://cal.vet.upenn.edu/projects/saortho/chapter_72/72ma
st.htm
 http://www.dcavm.org/dec99.htm