Purpose: Patients with spina bifida have smaller kidneys than healthy individuals. We evaluated the correlation between small size and decreased renal function, and the possible role of growth hormone deficiency.
Materials and methods: A total of 54 patients (mean age 11.5 years, median 11, standard deviation +/- 4.52) were healthy except for neuropathic bladder due to spina bifida. Renal function was evaluated with mercaptoacetyltriglycine renal scintigraphy and creatinine clearance. Renal anatomy was evaluated with renal ultrasound and voiding cystourethrography. Serum insulin-like growth factor-1 (IGF-1) levels were measured in all patients with immunoradiometric assay. Renal measurements in our patients were compared using the Sutherland nomogram.
Results: A total of 22 patients (41%) had smaller kidneys than normal subjects and 31 appeared to have creatinine clearance values lower than 120 ml per minute per 1.73 m2. The statistical comparison between kidney size and creatinine clearance was significant (p <0.05, r = 0.381). Scintigraphic data showed total effective renal plasma flow less than 568 ml per minute per 1.73 m2 body surface area (normal mean value for age). Comparison between effective renal plasma flow and creatinine clearance was significant (p <0.05, r = 0.31). Serum levels of IGF-1 were normal for age in all patients (mean 332.06 ng/ml, median 303.4, range 39.4 to 732.3).
Conclusions: The kidneys are smaller in patients with spina bifida than in healthy subjects when compared using the Sutherland nomogram. There is a significant correlation between smaller renal length and decreased renal function in all patients, even in those who are healthy except for neurogenic bladder secondary to spina bifida. IGF-1 levels were normal for age, and, therefore, these patients had no growth hormone deficiency. These findings call into question the hypothesis that growth hormone deficiency contributes to smaller kidney size. Other hypotheses can be suggested, such as a defect of embryological growth secondary to malformation, or the result of a defect in homocysteine-methionine metabolism.