My patient with erythema multiforme has tested positive for Mycoplasma pneumoniae IgM antibody. Does this mean she has an acute M. pneumonia infection as the cause of her acute illness?

Not necessarily! Although detection of IgM in the serum of patients has proven valuable in diagnosing many infections during their early phase, particularly before IgG is detected, less well known is that false-positive IgM results are not uncommon. 1

More specific to M. pneumoniae IgM, false-positive results have been reported in 10-80% of patients without a clinical diagnosis of acute M. pneumoniae infection 2-4 and 3-15% of blood donors. 4

False-positive IgM results may also occur when testing for other infectious agents, such as the agent of Lyme disease (Borrelia burgdorferi), arboviruses (eg, Zika virus), and herpes simplex, Epstein-Barr, cytomegalovirus, hepatitis A and measles viruses. 1,5  

Reports of false positive IgM results include a patient with congestive heart failure and mildly elevated liver enzymes who had a false-positive hepatitis IgM which led to unnecessary public health investigation and exclusion from an adult day care center. 1 Another patient with sulfa rash had a false-positive measles IgM antibody resulting in callback of >100 patients and healthcare providers for testing!5

There are many potential mechanisms for false-positive IgM results, including polyclonal B cell activation, “vigorous immune response”, cross-reactive antibodies, autoimmune disease, subclinical reactivation of latent viruses, influenza vaccination, overreading weakly reactive results, and persistence of antibodies long after the resolution of the acute disease. 1,2

In our patient, a significant rise in M. pneumoniae IgG between acute and convalescent samples several weeks apart may be more helpful in diagnosing an acute infection accounting for her erythema multiforme.

 

References

  1. Landry ML. Immunoglobulin M for acute infection: true or false? Clin Vac Immunol 2016;23:540-5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4933779/
  2. Csango PA, Pedersen JE, Hess RD. Comparison of four Mycoplasma pneumoniae IgM-, IgG- and IgA-specific enzyme immunoassays in blood donors and patients. Clin Micro Infect 2004;10:1089-1104. https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(14)63853-2/pdf
  3. Thacker WL, Talkington DF. Analysis of complement fixation and commercial enzyme immunoassays for detection of antibodies to Mycoplasma pneumoniae in human serum. Clin Diag Lab Immunol 2000;7:778-80. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC95955/
  4. Ryuta U, Juri O, Inoue Y, et al. Rapid detection of Mycoplasma pneumoniae IgM antibodies using immunoCard Mycoplasma kit compared with complement fixation (CF) tests and clinical application. European Respiratory Journal 2012; 40: P 2466 (Abstract). https://erj.ersjournals.com/content/40/Suppl_56/P2466 
  5. Woods CR. False-positive results for immunoglobulin M serologic results: explanations and examples. J Ped Infect Dis Soc 2013;2:87-90. https://www.ncbi.nlm.nih.gov/pubmed/26619450

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My patient with erythema multiforme has tested positive for Mycoplasma pneumoniae IgM antibody. Does this mean she has an acute M. pneumonia infection as the cause of her acute illness?

Should my patient with suspected alcoholic hepatitis undergo liver biopsy?

Although a characteristic clinical history and biochemical pattern of liver injury can strongly suggest the diagnosis of alcoholic hepatitis (AH), a definitive diagnosis is confirmed with liver biopsy only. In fact, in 30% of patients clinically diagnosed as having AH, a liver biopsy may lead to an alternative diagnosis.1Understandably, many physicians are reluctant to proceed with biopsy in this fragile patient population given the associated risks, notably bleeding. For this reason, most patients with AH are clinically diagnosed without a liver biopsy. However, there are certain instances in which a biopsy can be helpful, including when:2

  • Diagnosis of AH is in doubt
  • Suspicion for another disease process that may be contributing in parallel to AH is high
  • Obtaining prognostic data or identification of advanced hepatic fibrosis or cirrhosis in AH is desired

Thus, liver biopsy findings may influence short- and long-term management in AH. For these reasons, the European Association for the Study of the Liver recommends consideration of a liver biopsy in patients with AH.3 To minimize the bleeding risk, the transjugular approach is preferred.

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References

  1. Mookerjee RP, Lackner C, Stauber R, et al. The role of liver biopsy in the diagnosis and prognosis of patients with acute deterioration of alcoholic cirrhosis. J Hepatol 2011; 55:1103-1111 Link
  2. Altamirano J, Miquel R, Katoonizadeh A, et al. A histologic scoring system for prognosis of patients with alcoholic hepatitis. Gastroenterology 2014;146: 1231-1239. PDF
  3. European Association for the Study of Liver. EASL clinical practical guidelines: management of alcoholic liver disease. J Hepatol 2012; 57:399-420. PDF

Contributed by Jay Luther, MD, Gastrointestinal Unit, Mass General Hospital, Boston, MA.

Should my patient with suspected alcoholic hepatitis undergo liver biopsy?