Severe myositis Flashcards
What happens to muscle bulk and reflexes in polymyositis?
they are preserved until very late
What is polymyositis?
inflammatory disorder causing symmetrical, proximal muscle weakness
What is thought to be the cause of polymyositis?
T-cell mediated cytotoxic process directed against muscle fibres
may be idiopathic or associated with connective tissue disorders
What serious condition is polymyositis associated with?
malignancy
How does dermatomyositis fit in with polymyositis?
it is a variant of the disease where skin manifestations are prominent, for example a purple (heliotrope) rash on the cheeks and eyelids
polymyositis + skin rashes
Which age group and gender is predominantly affected by polymyositis?
middle-aged
female:male 3:1
What are 6 clinical features of polymyositis?
- Proximal muscle weakness ± tenderness
- Raynaud’s
- Respiratory muscle weakness
- Interstitial lung disease e.g. fibrosing alveolitis or organising pneumonia
- Dysphagia
- Dysphonia
What kind of lung disease may be present in polymyositis?
interstitial lung disease e.g. fibrosing alveolitis or organising pneumonia
What are 5 important investigations to help diagnoise polymyositis?
- Elevated creatine kinase
- Other muscle enzymes (lactate dehydrogenase [LD], aldolase, AST and ALT) also elevated in 85-95% of patients
- EMG
- Muscle biopsy
- Anti-synthetase antibodies
- anti-Jo1 antibodies seen in pattern of disease with lung involvement, Raynaud’s and fever
Which type of polymyositis are anti-synthetase antibodies e.g. anti-Jo1 usually seen?
in the pattern of disease associated with lung involvement, fever and Raynauds
What is mnemonic to remember the elevated muscle enzymes in polymyositis?
CLAAA:
- Creatine kinase
- Lactate dehydrogenase
- Aldolase
- ALT
- AST
Which muscles are affected by weakness in polymyositis?
bilateral, proximal (hip and shoulder girdle)
Over what time period does weakness develop in polymyositis?
usually over weeks to months
What are 3 types of muscle groups that become involved in polymyositis later in the disease and what can this lead to?
- Pharyngeal muscles: dysphonia/dysphagia
- Oesophageal muscles: dysphagia
- Respiratory muscles: poor ventilation with type 2 respiratory failure
What are 2 differentials for polymyositis/dermatomyositis?
- Steroid or statin-iduced myopathy
- Thyroid disease
What are 8 features specific to the presentation of dermatomyositis?
- Heliotrope rash - lilac discolouration of eyelid skin in addition to periorbital oedema
- Photosensitive
- Gottron’s papules which are scaly, erythematous papules over knuckles and extensor surfaces of knees and elbows
- Macular erythematous rash generally found on the head and neck, trunk or hands
- Mechanic’s hands: extremely dry, scaly hands with linar cracks on palmar and lateral aspects of fingers
- Periungual (nailfold) erythema (capillary dilatation)
- Cutaneous vasculitis which can present as rashes and lead to ulcers
- Calcinosis
What are 4 extra-muscular features of polymyositis and dermatomyositis?
- Systemic upset (fever/ tiredness/ malaise/ weight loss)
- Joints (polyarthralgia)
- Pulmonary (interstitial lung disease)
- Cardiovascular (Raynaud’s phenomenon and myocarditis)
What proportion of cases of poly/dermatomyositis are secondary to an underlying malignancy?
5-15%
Of dermatomyositis and polymyositis, which has the stronger association with malignancy?
dermatomyositis
What are the 5 types of cancers most commonly associated with polymyositis/dermatomyositis?
- Lung
- Oesophagus
- Breast
- Colon
- Ovary
What are the 3 most important initial tests to perform on all patients in whom you suspect a diagnosis of poly/dermatomyositis?
- Muscle-derived serum elevation; creatine kinase is most sensitive indicator, level usuall paralells disease activity
- EMG
- Muscle biopsy - definitive diagnosis
What are 2 advantages of measuring creatine kinase in suspected poly/dermatomyositis?
- Most sensitive indicator
- Level usually parallels disease activity, particularly in polymyositis
What is the role of EMG when investigating poly/dermatomyositis?
confirms the myopathic pattern of the disorder and excludes a primary neurogenic disorder
What do neurogenic disorders show on EMG (unlike in myositis)?
short duration and low amplitude polyphasic motor units on voluntary activation
What investigation makes the definitive diagnosis of poly/dermatomyositis?
muscle biopsy
What will muscle biopsy show in polymyositis?
endomysial inflammatory infiltrates
What will muscle biopsy show in dermatomyositis?
perivascular, perimysial inflammatory infiltrate
What must investigations look for in dermato/polymyositis, as well as to make the initial diagnosis?
look for underlying malignancy
When polymyositis is associated wtih lung cancer how can it manifest?
para-neoplastic syndrome
What is the mainstay of treatment of dermato/polymyositis?
corticosteroids - start at high dose
creatanine kinase monitored to guide rate of tapering the dose
What is used to guide the tapering dose of corticosteroids in poly/dermatomyositis?
creatanine kinase
What drugs may be needed as an add-on to corticosteroid treament in myositis?
additional immunosuppressants such as methotrexate or azathioprine as a steroid sparing agent
Which drug occasionally helps with skin disease in dermatomyositis?
hydroxychloroquine
What can be used to treat dermato/polymyositis in addition to pharmacological therapy?
physiotherapy
What factor makes dermatomyositis more likely to be associated with cancer?
if they are of increased age
What antibody are 80% of dermatomyositis patients positive for?
ANA (anti-nuclear antibody)
In addition to ANA, what other type of antibodies are a proportion of patients with dermatomyositis positive for and what are 3 examples?
30% have antibodies against aminoacyl-tRNA synthetases (anti-synthetase antibodies) including:
- antibodies against histidine-tRNA ligase (also called Jo-1)
- antibodies to signal recognition particle (SRP)
- anti-Mi-2 antibodies
