Epidemiology and Risk Factors for Pain In Children and Adolescent with Sickle Cell Anemia.

Pain crises are the most common symptom experienced by individuals with sickle cell anemia (SCA). Frequency of pain crises varies significantly and high rate is a risk factor for higher mortality in adults with SCA. The risk factors for pain crises in children and adolescents with SCA are not completely understood. To determine factors associated with frequent severe pain crises, we analyzed the cohort of children and adolescents with SCA who were enrolled in the prospective study “The Pulmonary Hypertension and the Hypoxic Response in SCD (PUSH)”. All children were evaluated in their steady, non-crisis state.

Family-reported history of number of severe pain crises in the preceding 12 months was recorded prospectively in 365 children and adolescents with SCA. Severe pain crises were defined as painful vaso-occlusive episodes requiring evaluation in Emergency Department (ED) or in-patient hospitalization. Lifetime history of red cell transfusions, echocardiography, and laboratory studies were obtained. Clinical and laboratory characteristics of study subjects who had ≥3 severe pain crises in the preceding year were compared to subjects with < 3 severe pain crises.

Study subject ranged in age from 3–20 years and 175 (48%) were female. Seventy two children (20 %) had ≥3 severe pain crises in the preceding year (frequent pain crisis group); 293 (80%) children had < 3 severe pain crises (infrequent pain crisis group), including 224 (61%) subjects who had no admissions/ ED visits for pain. Associated factors for frequent pain crisis included older age (odds ratio 1.2; 95% confidence interval 1.12–1.35; P <0.001) and α-thalassemia trait (odds ratio 3.22; 95% confidence interval 1.55–6.69; P =0.002) while higher steady state serum lactate dehydrogenase (LDH) was associated with infrequent pain crisis (odds ratio 0.35; 95% confidence interval 0.13–0.98; P =0.045). In a group of patients without α-thalassemia trait, older age and low LDH were linked to frequent pain crisis. Subjects in the frequent pain crisis group had higher median hemoglobin (9.0 vs. 8.5 gm/dL; p=0.003) and higher ferritin (median 455 vs. 191 ng/mL; p=0.008). Higher ferritin in the frequent pain crisis group was mirrored by the higher percentage who reported >10 lifetime transfusions (42% vs. 22%; p=0.001). Median tricuspid regurgitation jet velocity (TRV) was higher in the frequent pain crisis group (2.41 vs. 2.31; p= 0.001) but the proportion of children with TRV>2.5 was not different (19.4% vs.11.5% in infrequent crises group; p=0.09). Hydroxyurea use was not different between the groups (51% vs. 40%; p=0.08) nor was fetal hemoglobin (10% vs. 12%; p=0.2).

The occurrence of severe pain crisis varies among children and adolescents with SCA with a large number of children experiencing no severe painful episodes. Consistent with the Cooperative Study of Sickle Cell Disease report, the risk of severe pain crisis increases with age. Individuals with α-thalassemia trait are likely to experience more frequent pain crises possibly related to higher hemoglobin concentration and viscosity. However, even after controlling for α-thalassemia trait, children and adolescents who reported more frequent severe pain crises showed evidence of less hemolysis, consistent with a hypothetical model associating the hemolytic subphenotype of SCA with less frequent vasoocclusive pain crises. Further studies are indicated to identify the molecular mechanisms of pain in sickle cell anemia.

No relevant conflicts of interest to declare.