Overview
Mycoplasma pneumoniae is a cause of atypical pneumonia, particularly in younger people. It binds firmly to respiratory epithelial cells. It is associated with complications including erythema multiforme and cold autoimmune haemolytic anaemia.
Humans are the only hosts for Mycoplasma pneumoniae and transmission is via the respiratory route. Epidemics occur at 3- to 5-year intervals and their incidence can increase in late summer/early autumn.
Risk Factors
- Younger people (usually <30 years old)
- Overcrowding
- Exposure to a person with infection
- Smoking
Presentation
Overview
Mycoplasma pneumoniae infection has an incubation period of 2-3 weeks. It can present insidiously with:
- A prodrome of flu-like symptoms – fever, chills, malaise, myalgia, headaches
- Followed by cough and shortness of breath – children may have wheezing
- Pneumonia can develop in <10% of people
- Features of complications (discussed below)
Complications
Complications and their features include:
- Skin manifestations (~1/3) – particularly erythema multiforme and erythema nodosum:
- Thought to be due to bacterial skin invasion. In severe cases, Stevens-Johnson syndrome can occur.
- Cold autoimmune haemolytic anaemia:
- Due to cold agglutin antibodies against the I antigen which is present in red blood cells and respiratory epithelial cells.
- They may occur due to the attachment of Mycoplasma pneumoniae to respiratory epithelial cells.
- Neurological disorders – including Guillain-Barré syndrome and meningoencephalitis:
- May be seen up to 2 weeks post-infection and are thought to be autoimmune
- Bullous myringitis:
- Characterised by intensely painful bullae/vesicles on the tympanic membrane.
- Arthritis and arthralgia:
- May be seen acute infection and can persist for a long time post-infection
- Cardiovascular disorders – pericarditis and/or myocarditis:
- Due to the accumulation of inflammatory fluid in the pericardial space
- Gastrointestinal disorders – hepatitis, pancreatitis:
- Thought to be due to circulating IgM antibodies
- Renal disorders – glomerulonephritis:
- Due to the deposition of immune complexes in the glomeruli
Investigations
Overview
Some investigations include:
- Full blood count (FBC) – may show haemolytic anaemia
- Cold agglutinins test – may be positive
- Liver function tests (LFTs) – may show elevated transaminases
- Chest X-ray – may show bilateral consolidation
- Antibody serology – used for diagnosis, but retrospectively:
- Antibodies can take 2-4 weeks to develop, therefore Mycoplasma pneumoniae is often diagnosed retrospectively.
- Cultures are difficult and relatively insensitive.
Differential Diagnoses
Legionella pneumonia
- Although both can have flu-like symptoms, a dry cough, and deranged liver function tests, Legionella pneumonia is associated with lymphopenia and hyponatraemia.
Management
Overview
The antibiotics of choice are a macrolide (such as clarithromycin or erythromycin) or doxycycline.
Prognosis
- Infection is usually self-limiting and resolves over 3-10 days without treatment
- In most cases, no complications occur, however, many people have prolonged coughing for a few weeks
