Pericardial mass and cardiac tamponade associated with Mycoplasma pneumoniae
Editor – This interesting case report (Clin Med 2014;14: 549–50) raises the interesting issue of positive Mycoplasma serology and the interpretation of serology in general. The titre of the initial antibody, IgM, is the only Mycoplasma serology reported with the laboratory results in Table 1. This is usually reported as a titre (eg 1 in 40) although here is expressed as units. Low titres of Mycoplasma IgM are often false-positive results, thought to be due to problems of cross-reactivity with polyclonal IgM. Even in scientific studies, specificity and sensitivity of the test is suboptimal, and depends on the assay used.1 IgG is more reliable but the reliability of this test is based on an increase in titre between the acute and convalescent phase. A single positive IgG alone simply means that the patient had been exposed to Mycoplasma infection at some point, possibly years earlier. To determine if Mycoplasma infection may have contributed to causation in this case, it is essential that the authors report the initial and follow-up titres of IgG. It is not clear from the text that the case was discussed with their local infection specialist. Had they done so, I am sure this specialist would have pointed out to them the complexities of interpreting Mycoplasma IgM and the difficulties in presuming that Mycoplasma infection was a contributing factor in the clinical illness reported here. It is critical that your readers are not misinformed on this clinical condition and the difficulties in interpreting positive serology.
- © 2015 Royal College of Physicians
Reference
- 1.↵
- Beersma MF,
- Dirven K,
- van Dam AP,
- Templeton KE,
- Claas EC,
- Goossens H
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