Myocarditis
DEFINITION
Acute inflammation and necrosis of cardiac muscle (myocardium).
AETIOLOGY
Usually unknown (idiopathic).
Infection:
Viruses: e.g. Coxsackie B, echovirus, EBV, CMV, adenovirus, influenza.
Bacterial: e.g. post-streptococcal, tuberculosis, diphtheria, Lyme disease.
Fungal: e.g. candidiasis.
Protozoal: e.g. trypanosomiasis (Chagas disease).
Helminths: e.g. trichinosis.
Non-infective:
Systemic disorders (e.g. SLE, sarcoidosis, polymyositis), hypersensitivity myocarditis (e.g. sulphonamides).
Drugs:
Chemotherapy agents (e.g. doxorubicin, streptomycin)
Others:
Cocaine abuse, heavy metals, radiation.
EPIDEMIOLOGY
True incidence is unknown, as many cases are not detected at the time of acute illness. Coxsackie B virus is a common cause in Europe and the USA. Chagas disease is a common cause in South America.
HISTORY
Prodromal ‘flu-like’ illness, fever, malaise, fatigue, lethargy.
Breathlessness (pericardial effusion/myocardial dysfunction).
Palpitations.
Sharp chest pain (suggesting associated pericarditis).
EXAMINATION
Signs of concurrent pericarditis or complications: heart failure,
arrhythmia.
INVESTIGATIONS
Blood:
FBC (" WCC in infective causes), U&E, " ESR or CRP, cardiac enzymes (may be "). To identify the cause (viral or bacterial serology, antistreptolysin O titre, ANA, serum ACE, TFT).
ECG:
Non-specific T wave and ST changes, widespread saddle-shaped ST elevation in pericarditis.
CXR:
May be normal or show cardiomegaly with or without pulmonary oedema.
Pericardial fluid drainage:
Measure glucose, protein, cytology, culture and sensitivity.
Echocardiography:
Assesses systolic/diastolic function, wall motion abnormalities, pericardial effusion.
Myocardial biopsy:
Rarely required (result does not influence management).
MANAGEMENT
Supportive:
Bed rest, treatment of complications (heart failure, arrhythmias), pericardial drainage for compromising pericardial effusion.
Steroids and immunosuppressants have been used in severe cases but are of unproven benefit.
Surgical:
Cardiac transplantation for severe cases.
COMPLICATIONS
Severe cases can lead to chronic inflammation, cardiac failure. Resolution of inflammation with different degrees of residual dilated cardiomyopathy, arrhythmias and death.
PROGNOSIS
Usually mild and self-limiting. Recovery is variable in patients with severe acute myocarditis.
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