Eur J Pediatr (2008) 167:613–619 DOI 10.1007/s00431-008-0686-1 REVIEW Symptomatic asymmetry in the first six months of life: differential diagnosis Jacqueline Nuysink & Ingrid C. van Haastert & Tim Takken & Paul J. M. Helders Received: 11 October 2007 / Revised: 27 January 2008 / Accepted: 29 January 2008 / Published online: 4 March 2008 # The Author(s) 2008 Abstract Asymmetry in infancy is a clinical condition with a wide variation in appearances (shape, posture, and movement), etiology, localization, and severity. The preva- lence of an asymmetric positional preference is 12% of all newborns during the first six months of life. The asymmetry is either idiopathic or symptomatic. Pediatricians and physio- therapists have to distinguish symptomatic asymmetry (SA) from idiopathic asymmetry (IA) when examining young infants with a positional preference to determine the prognosis and the intervention strategy. The majority of cases will be idiopathic, but the initial presentation of a positional prefer- ence might be a symptom of a more serious underlying disorder. The purpose of this review is to synthesize the current information on the incidence of SA, as well as the possible causes and the accompanying signs that differentiate SA from IA. This review presents an overview of the nine most prevalent disorders in infants in their first six months of life leading to SA. We have discovered that the literature does not provide a comprehensive analysis of the incidence, characteristics, signs, and symptoms of SA. Knowledge of the presented clues is important in the clinical decision making with regard to young infants with asymmetry. We recommend to design a valid and useful screening instrument. J. Nuysink (*) : T. Takken : P. J. M. Helders Department of Pediatric Physical Therapy & Exercise Physiology, Wilhelmina Children’s Hospital, University Medical Center, KB 02.056.0, P.O. Box 85090, 3508 AB Utrecht, The Netherlands e-mail: j.nuysink@umcutrecht.nl I. C. van Haastert Department of Neonatology, Wilhelmina Children’s Hospital, University Medical Center, Utrecht, The Netherlands Keywords Infant . Symptomatic asymmetry . Etiology . Differential diagnosis . Screening . Torticollis . Plagiocephaly Abbreviations SA Symptomatic asymmetry IA Idiopathic asymmetry DP Deformational plagiocephaly CMT Congenital muscular torticollis CP Cerebral palsy Introduction The objective of this descriptive review is to determine and classify the possible causes of asymmetry seen in young infants who have an asymmetric head and/or body posture, as well as to present an overview of the nine most prevalent disorders in infants in the first six months of life leading to the diagnosis of symptomatic asymmetry (SA). Asymmetric infants form an increasing and complicated group of children seen by professionals from various clinical specialties, such as well baby clinic physicians, pediatri- cians, pediatric physiotherapists, orthopedic surgeons, and plastic surgeons [4, 6, 19, 37, 50, 61]. Asymmetry in infancy is a mostly benign symptom, but in this early phase of life, the differential diagnostics are extensive. The background of the professional influences the way in which associated clinical problems are evaluated. A screening instrument would be helpful. The first step in this process is to synthesize the current information in the literature about differential diagnostics. Twelve percent of all Dutch newborns develop a positional preference in the first few months of life,