Mycoplasma pneumoniae

is a cause of atypical pneumonia that often affects younger patients. It is associated with a number of characteristic complications such as erythema multiforme and cold autoimmune haemolytic anaemia. Epidemics of Mycoplasma pneumoniae classically occur every 4 years. It is important to recognise atypical pneumonia as it may not respond to penicillins or cephalosporins due to it lacking a peptidoglycan cell wall.

Features

• the disease typically has a prolonged and gradual onset
• flu-like symptoms classically precede a dry cough
• bilateral consolidation on x-ray
• complications may occur as below

Complications

• cold agglutins (IgM): may cause an haemolytic anaemia, thrombocytopenia
• erythema multiforme, erythema nodosum
• meningoencephalitis, Guillain-Barre syndrome and other immune-mediated neurological diseases
• bullous myringitis: painful vesicles on the tympanic membrane
• pericarditis/myocarditis
• gastrointestinal: hepatitis, pancreatitis
• renal: acute glomerulonephritis

Investigations

• diagnosis is generally by Mycoplasma serology
• positive cold agglutination test → peripheral blood smear may show red blood cell agglutination

Management

• doxycycline or a macrolide (e.g. erythromycin/clarithromycin)