Ultrasound in the Diagnosis of ADPKD in Childhood
ABSTRACT & COMMENTARY
Synopsis: Ultrasonographic imaging of the kidneys is the screening study of choice for the diagnosis of autosomal dominant polycystic kidney disease in children. The current study describes the limitations of ultrasonography when compared to gene linkage and analysis, especially in young children.
Source: Gabow PA, et al. Utility of ultrasonography in the diagnosis of autosomal dominant polycystic kidney disease in children. J Amer Soc Neph 1997;8:105-110.
Gabow et al at the university of colorado studied 106 children under the age of 18 known to be at 50% risk for autosomal dominant polycystic kidney disease (ADPKD) in order to determine the diagnostic reliability of ultrasonography (US) by comparing it to diagnosis by gene linkage and analysis (GLA). It is established that US is an accurate and useful tool in the diagnosis of ADPKD in patients over the age of 30, but its reliability in the pediatric age group is unknown. An at-risk child was considered to have the clinical diagnosis of ADPKD if sonography identified a renal cyst. The ages of the patients ranged from birth to 17 years at the time of the initial US (median age, 9 years). Sixty-two children (58%) had ADPKD documented by GLA. Fourteen of these had a negative US, reflecting a false-negative rate of 25%, and two of 44 GLA-negative children had a positive US, reflecting a false-positive rate of 5%. Of the 14 with initial negative US, eight subsequently had positive studies. In the two children with false-positive US, one had a medullary pyramid misinterpreted as a cyst, and the other had a single cortical cyst not related to ADPKD. US is an important tool for the clinical diagnosis of ADPKD in children as long as one accepts a significant false-negative rate and shares this limitation with the patient and family.
COMMENT BY THOMAS L. KENNEDY, MD, FAAP
Parents who have a family history of ADPKD are generally aware there is a risk to their children and frequently ask their pediatrician for advice concerning testing to attempt to either establish or exclude the diagnosis. Because it is uncommon for ADPKD to be of clinical significance in the pediatric age group, the family’s query is likely to be met with a blank look. At this uncomfortable moment, questions come to mind, such as what is the best method and best time for diagnosis? Does a simple blood test exist? Is there a reliable imaging study and, if so, which one? Is there a minimum age before which diagnosis is not possible? Should the child be referred to a nephrologist or urologist or to a genetic counseling clinic?
This study clarifies some of these questions. Genetic confirmation by GLA, although definitive, is not readily clinically available at present. The technology of US is well refined and can readily identify even very small cysts (10 mm in diameter) and aid in the diagnosis of ADPKD. Although US is the imaging and screening study of choice for identifying ADPKD in childhood, it must be recognized that there is a significant incidence of false negatives (1 in 4), and that a false negative is more likely the younger the child. Therefore, any child at risk for ADPKD with a single negative US requires ongoing follow-up and subsequent US studies to monitor the possible appearance of cysts. The family must be counseled with this possibility in mind.