Interrater Reliability in the Assessment of Muscle Tone of Infants and Children

The assessment of muscle tone is an integral part of the neurological examination of infants and children. Detection of an alteration in muscle tone aids in establishing a diagnosis, is used as justification for therapeutic services, and is viewed as an indicator of neurological change. The purpose of this study was to establish the degree of interrater reliability among pediatric physical therapists in the assessment of muscle tone in children age birth to three years. Six physical therapists were raters. Each rater was randomly assigned to nine evaluations. Eighteen children were evaluated by a group of three raters. The testing protocol included observation of the child's spontaneous movement for 10 minutes, followed by a 10 minute assessment period in which the raters individually assesssed the child using the rater's preferred method of evaluation. Following the evaluation, each rater completed a tone summary form, scoring: (1) clinical impression of abnormality, (2) tone sumary statement, and (3) tone type and severity for the four extremities and the neck and trunk. Total percent agreement on clinical impression of abnormality was 61.1%; agreement on tone summary was 55.6%; agreement for severity of body part ranged from 40.7% to 51.9% (78.9% of the time agreement on severity varied by zero or one point). As this represents low reliability in the clinical setting, therapists should be very cautious regarding clinical decisions based on an assessment of muscle tone. Interrater reliability was affected by: (1) the lack of a standard technique of method for assessing tone; (2) the lack of consistant terminology to describe tonal state and severity; (3) specific problems with the scoring method for tone summary; and (4) lack of a category for abnormal fluctating tone.