Myopathic disoders Flashcards
What is polymyositis?
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
How common is polymyositis?
Very rare
Affects adults and children
More common in women
What can increase your risk of polymyositis?
Viral infection - coxsackie, rubella, influenza
Genetic predisposition - HLA-B8/DR3
How does polymyositis present?
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
How can you diagnosed polymyositis?
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
How is polymyositis treated?
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
What is dermatomyositis?
Rare muscular disorder of unknown aetiology in which there is inflammation and necrosis of skeletal muscle fibres with skin involvement
How common is dermatomyositis?
Very rare
Affects adults and children
More common in women
What can increase your risk of dermatomyositis?
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
How does dermatomyositis present?
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
How is dermatomyositis diagnosed?
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
How is dermatomyositis treated?
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
What is inclusion boy myositis?
Progressive muscle disorder characterised by muscle inflammation, weakness, and atrophy
Inflammatory myopathy
Develops in adulthood after 50
How does inclusion body myositis present?
Progressive weakness of legs, arms, fingers, and wrists
Some have dysphagia
Classic picture wasting of forearm flexors and quads
Some patients also have neuropathy
How do you treat inclusion body myositis?
Exercise
Fall prevention
PT, OT, SALT
Not usually responsive to immunosuppressants
What is Duchenne muscular dystrophy?
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
How common is Duchenne muscular dystrophy?
Diagnosis often between ages 3-6
Female carriers can have proximal myopathy and 20% risk of cardiomyopathy
How does Duchenne muscular dystrophy present?
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
How is Duchenne muscular dystrophy treated?
Gene therapy treatments starting to become available
Otherwise little treatment
What is myotonic dystrophy?
Autosomal dominant muscular dystrophy
Trinucleotide repeat disorder
How does myotonic dystrophy present?
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
