Myopathic disoders

Question 1

What is polymyositis?

Answer 1

Rare muscular disorder of unknown aetiology in which there is inflammation and necrosis of skeletal muscle fibres associated with an increased risk of lung and ovarian cancers

Question 2

How common is polymyositis?

Answer 2

Very rare
Affects adults and children
More common in women

Question 3

What can increase your risk of polymyositis?

Answer 3

Viral infection - coxsackie, rubella, influenza

Genetic predisposition - HLA-B8/DR3

Question 4

How does polymyositis present?

Answer 4

Symmetrical muscle weakness and wasting affecting proximal muscles of shoulder and pelvic girdle
Difficulty squatting, going upstairs, rising from a chair and raising hands above head
Pain and tenderness uncommon
Involvement of pharyngeal, laryngeal, and respiratory muscles leading to dysphagia, dysphonia, and respiratory failure
Arthralgia in small joints of hands
Raynaud’s

Question 5

How can you diagnosed polymyositis?

Answer 5

Muscle biopsy – fibre necrosis, inflammatory cell infiltrates
Muscle enzymes – serum creatine kinase, aminotransferases, lactate dehydrogenase, aldolase all raised
ESR increased
Serum antibodies – ANA and RF positive, anti-Jo positive
Electromyography to detect typical muscle changes – short polyphasic motor potentials, spontaneous fibrillation and high frequency repetitive discharges
MRI to detect abnormally inflamed muscles
Normocytic normochromic anaemia

Question 6

How is polymyositis treated?

Answer 6

Steroids – continues for at least 1 month after clinically and enzymatically inactive, tapered down slowly
Azathioprine/methotrexate/cyclophosphamide/mycophenolate
Biologic therapies eg rituximab
Bed rest combined with exercise programmes
Hydroxychloroquine or topical tacrolimus

Question 7

What is dermatomyositis?

Answer 7

Rare muscular disorder of unknown aetiology in which there is inflammation and necrosis of skeletal muscle fibres with skin involvement

Question 8

How common is dermatomyositis?

Answer 8

Very rare
Affects adults and children
More common in women

Question 9

What can increase your risk of dermatomyositis?

Answer 9

Viral infections of coxsackie, rubella, influenza
Genetic predisposition – HLA-B8/DR3
Idiopathic/associated with ConnT disorders
Associated with malignancy – breast, lung, ovary, stomach, intestine, nasal cavity, throat, pancreatic, bladder, Hodgkin’s lymphoma

Question 10

How does dermatomyositis present?

Answer 10

Skin involvement
- Photosensitive macular rash over back and shoulders
- Heliotrope rash around eyes
- Gottron’s papules - rough and red papules over extensor surfaces of fingers
- Nasal fold capillary dilatation and haemorrhages
Proximal muscle weakness
Respiratory muscle weakness
Arthralgia, dysphagia
Raynaud’s
Interstitial lung disease eg fibrosing alveolitis

Question 11

How is dermatomyositis diagnosed?

Answer 11

Muscle enzymes – serum CK raises, aminotransferases raised, lactate dehydrogenase raised, aldolase raised
EMG
Muscle biopsy – fibre degeneration and internalisation of sarcolemmal nuclei, inflammatory cell infiltrates
ANA positive in 60%
Jo-1 positive
ESR not raised

Question 12

How is dermatomyositis treated?

Answer 12

Steroids – continues for at least 1 month after clinically and enzymatically inactive, tapered down slowly
Azathioprine/methotrexate/cyclophosphamide/mycophenolate
Biologic therapies eg rituximab
Bed rest combined with exercise programmes
Hydroxychloroquine or topical tacrolimus

Question 13

What is inclusion boy myositis?

Answer 13

Progressive muscle disorder characterised by muscle inflammation, weakness, and atrophy
Inflammatory myopathy
Develops in adulthood after 50

Question 14

How does inclusion body myositis present?

Answer 14

Progressive weakness of legs, arms, fingers, and wrists
Some have dysphagia
Classic picture wasting of forearm flexors and quads
Some patients also have neuropathy

Question 15

How do you treat inclusion body myositis?

Answer 15

Exercise
Fall prevention
PT, OT, SALT
Not usually responsive to immunosuppressants

Question 16

What is Duchenne muscular dystrophy?

Answer 16

Severe type of muscular dystrophy primarily affecting boys as x-linked recessive with dystrophin gene
Muscle weakness that usually begins around 4 and worsens quickly

Question 17

How common is Duchenne muscular dystrophy?

Answer 17

Diagnosis often between ages 3-6

Female carriers can have proximal myopathy and 20% risk of cardiomyopathy

Question 18

How does Duchenne muscular dystrophy present?

Answer 18

Difficulty walking and developing calf pseudohypertrophy
Scoliosis
Intellectual impairment
Cardiomyopathy
Reduced night vision
Wheelchair bound by early adolescence and unlikely to live beyond 30
Death usually from cardiomyopathy
Muscle loss typically occurs first in thighs and pelvis followed by arms

Question 19

How is Duchenne muscular dystrophy treated?

Answer 19

Gene therapy treatments starting to become available

Otherwise little treatment

Question 20

What is myotonic dystrophy?

Answer 20

Autosomal dominant muscular dystrophy

Trinucleotide repeat disorder

Question 21

How does myotonic dystrophy present?

Answer 21

Myotonic facies – long and haggard
Frontal balding
Bilateral ptosis
Cataracts
Dysarthria
Myotonia – impaired muscle relaxation
Weakness affecting legs then arms (distal)
Mild mental impairment
Diabetes
Testicular atrophy
Cardiac - heart block – long PR interval – cardiomyopathy, mitral valve prolapse, IHD, diastolic HF
Dysphagia
Thyroid enlargement