Myopathies Flashcards
What are myopathies?
Myopathies = conditions diverse in aetiology grouped together because of a predominant impact on muscle
What are the different categories of disease which effect muscles?
Neurogenic disease = disease of peripheral nerves or motor neurons causes secondary atrophy of skeletal muscle
Inherited myopathies (including muscular dystrophies and metabolic defects resulting in myopathy)
Acquired myopathies
Describe the different types of myopathies and some of the causes?
Inherited myopathies (including muscular dystrophies and metabolic defects resulting in myopathy)
Acquired myopathies:
-Immune mediated (polymyositis, dermatomyositis, SLE, polymyalgia rheumatica, inclusion body myositis)
- Non inflammatory/endocrine: Hyper/hypo thyroid, Cushings, hyper/hypo parathyroidism, electrolyte disturbances (hypercalcaemia, hypokalaemia)
- Toxic and cachectic: Alcohol and certain drugs
- Infectious: Mostly viral.
Define muscular dystrophies?
Genetically predetermined diseases of muscle that generally result in progressive degeneration
What is the aetiology and pathology of Duchenne’s Muscular Dystrophy?
Duchenne muscular dystrophy:
X-linked recessive disorder, hence almost exclusively seen in males caused by mutation in dystrophin gene
A protein which normally helps anchor the muscle fibres to the extracellular matrix.
How does Duchenne’s usually present?
Its is often diagnosed between the ages of 3 -7 due to a gross motor delay and the demonstration of Gower’s sign.
Other classical signs include calf pseudohypertrophy due to fatty replacement of muscle.
How is Duchenne’s diagnosed?
Extremely raised CK.
Muscle biopsy.
Genetic tests for the most common genes.
Describe the natural history of Duchenne’s?
Poor prognosis
Often wheelchair bound by 12.
Affects cardio and respiratory function in late teens.
Patients usually die in their 20’s/30’s due to complications of their poor respiratory cardio function.
What is myotonic dystrophy?
It is an autosomal dominant condition characterised by muscle weakness and wasting.
Those with the disease have prolonged muscle contractions (myotonia) and are not able to relax certain muscles after use. (Unable to ungrip there hand)
Usually affects individuals in 20-50’s onset of the disease becomes earlier in each generation.
Other symptoms include:
- cataracts
- developmental delay and mild learning difficulty
- balding and development of infertility
- cardiomyopathy
What is spinal muscular atrophy?
It is an autosomal recessive condition causing:
- degeneration of the anterior horn cells
- leading to progressive weakness and wasting of skeletal muscles
There are 3 different types:
SMA 1/2/3
Type 1: most severe, children never sit unaided die of respiratory failure within 12 months
Type 2: Children will sit but never walk
Type 3: Children will walk but will present with symptoms later in life
What is polymyositis and how does it present?
It is a connective tissue disease characterised by inflammation of muscles.
It classically present with diffuse proximal muscle weakness as well as fatigue and myalgia.
The weakness tends to occur over weeks to months and gets gradually worse, however it may differ from week to week.
What is dermatomyositis and how does it present?
It is again a connective tissue disease characterised by inflammation of muscles.
It presents similarly to polymyositis in terms of the pattern of muscle weakness however also has additional features of:
- a heliotrope rash over the eyelids
- may have some calcinosis
- may have symptoms of fever and weight loss
Which conditions are associated with polymyositis and dermatomyositis?
Closely related to other connective tissue diseases and thought to have some crossover (Sjogren’s, SLE, RA and systemic sclerosis)
Other autoimmune disorders (myasthenia gravis and hashimoto’s)
Can present as a paraneoplastic syndrome paticulraly in dermatomyositis.
Which malignancies are associated with dermatomyositis?
Roughly 10-20% of patients with dermatomyositis have an underlying malignancy.
Breast cancer, lung cancer, ovarian carcinoma and gastric carcinoma are usually implicated.
How does inclusion body myositis differ in presentation to polymyositis?
Very similar presentation.
However usually only in more elderly patients at least older than 50.
More commonly affects distal muscles and it may be asymmetrical in nature. (can also affect proximal muscles)
