Idiopathic Short Stature: Reflections on Its Definition and Spontaneous Growth

Background: Despite clarification of the term idiopathic short stature (ISS) provided by an international consensus group, several points of discussion remain. Methods and Results: Various cut-off limits can be used for the definition of ‘short’, and in the absence of recent population-based references, decisions have to be taken about which reference to use, whether corrections for secular trend have to be made, and which references should be used for ethnic minorities. For the definition of ‘idiopathic’, decisions have to be taken regarding which disorders should be excluded and by which tools; how to deal with the fluid border between ISS and persistent short stature after being born small for gestational age; and which limit of disproportion is acceptable. Conclusions: Distinguishing between the two subclasses of ISS, familial short stature (FSS) versus non-familial short stature (non-FSS), requires a decision as to which of the various formulas for the parent-specific lower limit of height standard deviation score should be used, particularly when comparing final height with prepubertal height, predicted adult height, and target height. The distinction between FSS and non-FSS is also important for evaluating spontaneous growth in children with ISS.