Myopathies (acquired) Flashcards
What are some drug causes of myopathy?
Glucocorticoids – steroids increase the breakdown of muscle proteins leading to atrophy
Statins – some people possess certain genes of a particular SNP that increases the risk of developing myopathy, when taking high dose statins ie simvastatin; also has an interaction with grapefruit juice and other drugs that increase the risk of rhabdomyolysis by increasing the plasma concentration of simvastatin
Alcoholic
Narcotics
What are 4 inflammatory myopathies?
Dermatomyositis:
1/100,000; 40s-50s; F>M
Unknown cause; possible autoimmune disease or a result of a viral infection also as a paraneoplastic syndrome (ovarian/breast/lung)
Inflammation of the perimysium; humorally mediated angiopathy
Polymyositis:
F>M
Unknown cause; possible paraneoplastic Inflammation of the endomysium; mediated by cytotoxic T cells with an unknown autoantigen
Inclusion body myositis (IBM):
Muscle weakness in quadriceps, forearm and below knee – foot drop; more common in men and occurs mostly after age 50
Post-infectious reactive myositis:
Can occur after some viral infections; usually mild and settles without treatment
What are some endocrine/metabolic causes of myopathy?
Thyroid – thyrotoxic:
NMJ disorder developing due to over production of thyroxine
Parathyroid:
Primary hyperparathyroidism, secondary HPT due to renal failure and osteomalacia may all cause mild proximal weakness w/normal or slightly elevated CK due to hypercalcaemia/hypomagnesia; also vitamin D deficiency
Adrenal; Pituitary
What is rhabodomyolysis?
Rapid breakdown of skeletal muscle; most likely to to crush injury (earthquake), strenuous exercise, medication or drug abuse; infection, heat stroke, prolonged immobilisation (‘long lies’ in the elderly), limb ischemia, snake bite
What is a general presentation for myopathy?
Muscle weakness, cramps/stiffness, tetany
How does dermatomyositis present?
Skin rash – heliotrope (purple/lilac/red around eyes or upper chest/back; face/arms/thighs/hands); Gottron’s sign (red/violet, scalym raised papules on MCP/IP joints or other bony prominences)
Progressive muscle weakness – occurring suddenly or over several months – proximal weakness
Weight loss, fever
Light sensitive rash
Systemic - breathing difficulty, possible arrhythmias
Increased risk of malignancy
How do you investigate and manage dermatomyositis?
Diagnosis:
Hx/examination, bloods – CK/LDH/aldolase/ANA+ve/other specific autoAbs etc, EMG and muscle biopsy
Management: PT/orthotics, heat therapy, corticosteroids (PO/IV) +/- methotrexate/azathioprine +/- IVIg +/- rituximab; hydroxychloroquine – rashes
No cure
How does polymyositis present?
Proximal muscle weakness – including flexion of neck and torso; hip extensors often severely affected – climbing stairs/chairs; possible pain; comes on over weeks-months
Absent skin involvement – to differentiate from dermatomyositis
Dysphagia, oesophageal motility problems
Foot drop – in advanced cases
Systemic - breathing difficulty, possible arrhythmias
Increased risk of malignancy
How do you investigate and manage polymyositis?
Same as dermatomyositis…
How does rhabdomyositis present?
Muscle pain
Weakness
Vomiting (lots of symptoms secondary to electrolyte release from cells)
Confusion
Tea coloured urine – myoglobin
Arrhythmias
Renal failure – myoglobin is nephrotoxic; HTN; hypocalcaemia; DIC; shock; compartment syndrome
How do you investigate and manage rhabdomyolysis?
Urine dip +ve for blood but urinalysis finds no red cells; bloods – CK 1000U/L
