Figure 5.

Natural history of the disease and influence of screening and early treatment on outcome. Before the availability of specific therapy (and in health care shortage areas), congenital hypothyroidism if left untreated leads to growth failure and severe developmental delay (cretinism). Newborn screen using blood spots can diagnose the disease in the presymptomatic or preclinical phase, leading to early diagnosis and therapy in the neonatal period. In the absence of a screening test, patients with hypothyroidism can present with nonspecific symptoms, such as prolonged hyperbilirubinemia and constipation. Eventually, with the onset of specific symptoms, diagnosis is suspected, confirmatory tests are performed, and therapy is initiated. The difference between the time of early diagnosis and therapy with screening and the usual time of diagnosis and treatment is called the lead time. Diagnosis and therapy before a critical point in the natural history of the disease are more effective compared with delayed therapy.