MYOPATHIES Flashcards
What characterises a myopathy?
Weakness most often proximal
What are the clinical features of myopathies?
Weakness Loss of tone (often hard to distinguish) Wasting Preserved reflexes Myotonia Pain (rarely)
What is myotonia?
Persistence of contraction during attempted relaxation, often for several seconds.
How might you distinguish a lower motor neuron lesion from a myopathy?
Preservation of reflexes
Which of the myopathies display myotonia?
Myotonic distrophy
Paramyotonia congenita
Hyperkalaemic periodic paralysis
Congenital myotonia.
What are the X-linked myopathies?
Duchenne’s muscular dystrophy
Becker’s muscular dystrophy
Emery-Dreifuss dystrophy
What are the autosomal dominant myopathies?
Fascio-scapulo-humeral dystrophy
Scapulo-peroneal dystrophy
Myotonic dystrophy
What are the mitochondrial inherited myopathies?
Chronic progressive external opthalmoplegia
Kearns-Sayre syndrome
What is the underlying pathology of Duchenne muscular dystrophy?
Absence of dystrophin, a protein vital for connecting cytoskeleton of muscle to extracellular matrix.
By what age does Duchenne muscular dystrophy become apparent?
3-4
By what age is a child with Duchenne muscular dystrophy usually wheelchair bound?
10
What is the mean life expectancy of someone with Duchenne muscular dystrophy?
20
What complication will most patients with Duchenne muscular dystrophy die of?
Respiratory failure
Cardiomyopathy
Usually die in the third decade
What are the clinical features of Duchenne muscular dystrophy?
Initial proximal muscle weakness Pseudohypertrophy of calves due to accumulation of fat and connective tissue Gower's sign Waddling gait Difficulty standing up
What is Gower’s sign with reference to muscular dystrophy?
Patient attempts to climb their own legs when rising to an erect position.
What will blood tests of someone with Duchenne muscular dystrophy show?
Grossly elevated creatinine kinase.
What are the managements option for Duchenne muscular dystrophy?
Management is supportive
Steroids may provide short term improvement
What is the underlying pathology of Becker’s muscular dystrophy?
Altered dystrophin (as opposed to absent dystrophin in Duchenne)
When do the symptoms of Becker’s muscular dystrophy begin?
Around the age of 10
What are the clinical features of Becker’s muscular dystrophy?
Cramps associated with exercise
Cardiomyopathy often ends being worse than the skeletal weakness and patients often die before the skeletal problems overwhelm them.
What are the complications that might arise when someone with a muscular dystrophy undergoes surgery and has a general anaesthetic?
Malignant hyperthermia-type reaction with life threatening rhabdomyolysis.
What is rhabdomyolysis?
Damaged skeletal muscle breaks down rapidly, releasing proteins such as myoglobin into the bloodstream. This is toxic to the kidneys.
What is the most common adult myopathy?
Myotonic dystrophy with a prevalence of 1 in 7000
What is the underlying pathology of myotonic dystrophy?
Defects in the myotonin protein kinase gene.
How is the genetic transmission of myotonic dystrophy unusual relative to other disorders that exhibit anticipation?
Female transmission results in more severely affected offspring. In other disorders with anticipation (whereby successive generations are more severely affected), paternal transmission leads to more severely affected offspring.
What are the clinical features of myotonic dystrophy?
Progressive proximal and distal muscle weakness, especially in upper limbs Myotonia Myopathic faces Ptosis Cataracts Frontal balding Dysarthria and dysphagia Mild intellectual impairment Cardiomyopathy Testicular atrophy Glucose intollerance/diabetes
Between what ages do the symptoms of myotonic dystrophy usually develop?
20-50
What are the channelopathies?
Periodic paralyses - periods of sudden weakness with alterations in serum potassium levels. They are genetic mutations resulting in abnormalities of some ions chanels.
What are the clinical features of hypokalaemic periodic paralysis?
Attacks of generalised weakness following heavy carbohydrate meal or after a period of rest following strenuous exercise.
Potassium levels drop to around 3.0 mmol/L
What is the management for someone experiencing an acute attack of hypokalaemic periodic paralysis?
Potassium replacement
What is the prophylactic management of someone diagnosed with hypokalaemic periodic paralysis?
Potassium supplements
Potassium sparing diuretics
What are the clinical features of hyperkalaemic periodic paralysis?
Attacks of proximal weakness about 30 minutes after exercise or during fasting.
Potassium rises above 5.0 mmol/L
What is the management for someone experiencing an acute attack of hyperkalaemic periodic paralysis?
IV calcium gluconate
Salbutamol
What disease groups are polymyositis and dermatomyositis associated with?
Connective tissue disorders
Carcinomas
What are the clinical features of polymyositis and dermatomyositis?
30s-40s More common in women Proximal muscle weakness Pain Associated skin changes
What are the skin changes associated with polymyositis and dermatomyositis?
Macular erythema on the face - blue violet rash in peri-orbital area
Erythematous plaques - dorsal aspect of fingers
Nail-fold haemorrhages
Skin sensitive to the light
What are the complications associated with polymyositis and dermatomyositis?
Bulbar dysfunction
Respiratory muscle weakness
Interstitial fibrosing lung disease
What would blood tests reveal in someone with polymyositis or dermatomyositis?
Raised ESR
Very high CK
Autoantibodies - anto-Jo, antinuclear antibodies, RF, ENAs
What would EMG of someone with polymyositis or dermatomyositis reveal?
Myopathic picture, but may include fibrillations
What would the muscle biopsy of someone with polymyositis or dermatomyositis reveal?
Muscle fibre necrosis with an inflammatory infiltrate
What investigations should be ordered for someone with suspected polymyositis or dermatomyositis?
ESR
FBC
Autoantibodies - Anti-Jo
EMG
Biopsy
Investigation for underlying carcinoma (eg x-ray)
What are the treatment options for someone with polymyositis or dermatomyositis?
Corticosteroids
Other immunosuppressive drugs - azathioprine and cyclophosphamide
Removal of associated tumour
What is the most common cause of muscle disease in people aged over 50?
Inclusion body myositis
What are the clinical features of inclusion body myositis?
Weakness and wasting of flexor muscles of the forearm and hand - causing weak grip and grasp.
Some proximal muscle involvement
Oesophageal involvement
What common disease is inclusion body myositis associated with?
Diabetes
What is the main investigation for patients with suspected inclusion body myositis?
Muscle biopsy
What do people diagnosed with inclusion body myositis die of?
Respiratory compromise or aspiration pneumonia
What are the drugs that are known to induce myopathies?
Statins Steroids Chloroquine Amiodarone Doxorubicin Zidovudine (AZT)
What are the electrolyte and endocrine associated myopathies?
Thyrotoxicosis
Cushing’s syndrome
Hypokalaemia
Vitamin D deficiency
