English abstract
Acanthosis nigricans (AN) develops commonly in obese adults, yet its prevalence and metabolic significance in children and adolescents have not been determined. To address these issues, 100 obese children and adolescents enrolled in the obesity clinic at the Royal Hospital, Muscat, Oman, were chosen at random and examined, AN was observed in 33 of the study children (43%). The frequency and severity of AN increased significantly with increasing body mass index (BMI) in these children. Twenty patients with obesity and AN and 20 age-matched nonacanthotic obese children, randomly selected from the study children, were investigated. Their oral glucose tolerance and serum C-peptide responses to IV glucagon were evaluated. Circulating concentrations of free thyroxine (FT4), TSH, basal and ACTH-stimulated cortisol, testosterone, leutinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin were measured by radioimmunoassay (RIA). Children with AN exhibited higher basal and glucagon-stimulated C-peptide concentrations than the nonacanthotic obese group. Two hours after the oral load of glucose (1.75 g/kg), serum glucose concentration (6.3 ± 1.4 mmol/L) was higher in the acanthotic group versus the nonacanthotic group (5.2 ± 0.8 mmol/L). Impaired glucose tolerance was detected in two children with AN (10%), and in none of the nonacanthotic controls. Hypothyroidism was diagnosed in two (10%) children with AN (TSH = 109 and 18 mIU/mL and FT4 = 4.6 and 13.5 pmol/L respectively), while all the nonacanthotic children were euthyroid. Serum testosterone concentration was insignificantly lower in the acanthotic group (6.5 ± 3.9 ng/dL) versus the nonacanthotic children (8.3 ± 4.5 ng/dL). Basal serum LH, FSH and prolactin concentrations and basal and ACTH-stimulated cortisol levels did not differ between the two study groups. Plasma triglyceride concentration was significantly higher in the acanthotic group (1.43 ± 0.5 mmol/L) versus the nonacanthotic group (1.05 ± 0.45 mmol/L), and was correlated significantly with BMI (r = 0.466, P < 0.05). In conclusion, obesity is a significant risk factor for the development of AN in children. AN is a reliable skin marker of hyperinsulinemia in obese children and adolescents. The prevalence of impaired glucose tolerance (10%) and primary hypothyroidism (10%) appears to be higher in obese acanthotic children than in those without AN.
