Antistreptolysin-O Titers: Implications for Adult PANDAS

To the Editor: A diagnosis of pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS) is made when neuropsychiatric disease is precipitated by streptococcal infection (1). Antistreptolysin-O titers are an important tool for diagnosing recent streptococcal infection in patients with Sydenham’s chorea and PANDAS, since throat cultures are usually negative because of the latent onset of the neuropsychiatric disease. The upper limit for normal antistreptolysin-O titers is 200 IU/ml in children, but no normal upper limit exists for healthy adults. We propose that an antistreptolysin-O titer of 270 IU/ml is the significant upper limit for healthy adults. This finding will aid in the investigation and diagnosis of new cases of adult PANDAS.

Because of recent reports of cases of PANDAS in adults (2, 3), we measured antistreptolysin-O titers for 50 healthy adults to determine a normal adult range and investigated the number of healthy adults with higher than normal antistreptolysin-O titers. Fifty healthy adults (25 men and 25 women) were recruited from the staff of a pediatric hospital between November 2000 and May 2001; they had a mean age of 35.6 years (range=19–57). Subjects were excluded if there was a history of neurological, psychiatric, or autoimmune disease. The time of their most recent sore throat was recorded; 30% of the subjects had had a sore throat within the 6 months before the blood sampling. Blood samples were processed within 1 day of receipt, and antistreptolysin-O titers were measured by using a standardized nephelometry technique.

The subjects’ mean antistreptolysin-O titer was 122 IU/ml (range=50–376). Only 8% (four of 50) of the healthy adults had antistreptolysin-O titers higher than 200 IU/ml, 4% (two of 50) had titers over 300 IU/ml, and none had titers over 400 IU/ml. According to the upper limit of 200 IU/ml for a normal pediatric antistreptolysin-O titer, 8% (four of 50) of the healthy adults had “abnormal” titers. In this healthy adult group, the upper limit (95th percentile) for a normal antistreptolysin-O titer was 270 IU/ml.

The patients with recent cases of adult PANDAS both had highly elevated antistreptolysin-O titers of 1600 IU/ml (2) and 739 IU/ml (3). We conclude that streptococcal serology is a useful diagnostic tool for assessing the etiology of new cases of neuropsychiatric disease in adults and propose an antistreptolysin-O titer of 270 IU/ml as the upper limit of normal for adults.