Four cases of arthritis associated with Mycoplasma pneumoniae infection

Background: Mycoplasma pneumoniae infection is diagnosed commonly by marked elevation of serum antibodies, but this requires several days and consequently M. pneumoniae infection might be overlooked in some cases. Recently an ImmunoCard Mycoplasma rapid diagnosis test (IC) has been developed and used clinically. One of the advantages of this diagnosis test is that clinicians can recognize the infection by a single administration at the beginning of treatment. Methods: A total of 1033 children aged 1-15 years (average 2.0 years) were examined. The diagnosis of M. pneumoniae infection was made mainly on the basis of a positive reaction to the IC. Also where possible, particle agglutination (PA) was performed as a confirmatory test. Diagnosis was made on the basis of a fourfold or greater rise in the PA antibody titer by paired sera or an initial single PA titer > 1:320. Arthritis was diagnosed mainly on clinical symptoms. Additionally, ultrasonography (US) was conducted to confirm arthritis. In using US, arthritis was defined as an enlargement of the low echoic section or fluid retention inside the articular capsule. Results: IC was used in 1033 patients and results were positive in 348 (33.6%). Of these 348, there were 70 cases of pneumonia (20.1%) and four cases of arthritis (1.1%). IC was positive in all of the cases of arthritis, and in two of the four arthritis patients the PA titers were also useful for diagnoses. In three of four cases, US was performed and lesions were observed in two of three cases. Three of the four arthritis patients were infants and only one of these three had pneumonia. Conclusions: Using IC as a screening test, occult M. pneumoniae infections were discovered that would otherwise have been overlooked. These included two patients with US-proved arthritis. Arthritis in the absence of pneumonia may not be an unusual manifestation in infants infected by this organism.