Multiple limb lameness - myopathies

Question 1

What clinical signs with you see with myopathies?

Answer 1

clinical signs seen in polyarthritis (short strides, uneven gait, ect)

• Muscle atrophy
• Reduced muscle tone and local reflexes
• Dysphonia, dysphagia and regurgitation
• Megaoesophagus
• Pyrexia in inflammatory myopathies
• Pain in the temporal muscles and a reluctance to open the mouth with a masticatory muscle myositis (eosinophilic temporal myositis) or, after a few weeks, marked muscle atrophy

Question 2

what are the two general types of myopathies and the conditions within these?

Answer 2

Inflammatory myopathies
* Masticatory muscle myositis (MMM)
* Immune mediated disease e.g. Systemic Lupus Erythematosus or associated with polyarthritis
* Protozoal infections e.g. toxoplasma and neospora

Non inflammatory myopathies
* Genetic disorders e.g. Labrador myopathy (Floppy Labrador)
* Corticosteroid induced (endogenous and exogenous)
* Endocrine associated e.g. Cushing’s disease and hypothyroidism
* Metabolic abnormalities e.g. phosphofructokinase deficiency in the Springer spaniel

Question 3

How are myopathies diagnosed?

Answer 3

• clinical exam
• Blood samples including CPK (creatinine phosphokinase), electrolytes, lactate and pyruvate
• Thyroxine for hypothyroidism or MMM autoantibodies if suspect masticatory myositis
• Acetylcholine receptor antibody serology for myasthenia gravis (a neuromuscular disease)
• Toxoplasma and neospora serology
• Radiography for megaoesophagus
• **Muscle biopsy **(the most important diagnostic step)
• Skin biopsy if associated skin lesions seen in dermatomyositis in the Shetland and Rough Collie

Question 4

How are muscle biopsies taken for diagnosis of myopathies?

Answer 4

• These are take from the quadriceps, biceps femoris or triceps (0.5x0.5x1cm. portions)
• If suspect neuromuscular disease then cranial tibialis is a good muscle to biopsy
• Careful tissue handling is essential
• Samples are collected along the length of the fibres.
• They are placed in 10% formalin for H and E staining and also a fresh sample can be sent wrapped in moist gauzed and cooled for freezing prior to electron microcopy
• If in any doubt contact the lab prior to taking the samples

Question 5

what is the treatment for inflamatory myopathies?

Answer 5

• Antibiotics for protozoal infections e.g. clindamycin
• Immunosuppressive doses of corticosteroids if autoimmune disease suspected

Question 6

What needs to be on your differential list with a young animal (< 6 months) with generalised weakness or muscle atrophy/hypertrophy with accompanying dysphonia dysphagia and megaoesphagus?

Answer 6

centronuclear myopathy
(floppy labrador)

Question 7

there is Little evidence that dietary modifications help Metabolic associated myopathies, what are the treatemtn recomendations?

Answer 7

Avoid strenuous exercise and hyperthermia.

Question 8

What two breeds are predisposed to myotonias?
What is myoyonia?
how is it diagnosed?
What is the treatment?

Answer 8

• chow chows and miniature schnauzers - Also reported in the cat
• Increased tone and poor relaxation after muscle stimulation
• Persistent dimpling after percussion with a hammer
• Characteristic finding on electromyography (EMG)
• Treatment -procainamide mixelitine and phenytoin