INTRODUCTION

The cause of poor growth in childhood cancer survivors cannot always be identified. It often is caused by the toxic effects of chemotherapy, radiation effects on bone growth centers, or growth hormone deficiency, but it also may be caused by undiagnosed mild primary or central hypothyroidism.

In childhood cancer survivors, hypothyroidism is cause for poor growth and is a complication of therapy, most commonly due to radiation therapy to either the brain (central hypothyroidism) or neck (primary hypothyroidism) and less frequently due to chemotherapy. Early identification and treatment of hypothyroidism improves the quality of life and optimizes the final adult height of these patients.

The normal regulation of thyroid hormones and the diagnosis and treatment of hypothyroidism in childhood cancer survivors are reviewed here. Growth hormone (GH) deficiency after childhood cancer is discussed separately. (See "Growth failure after childhood cancer: Role of growth hormone deficiency".)

DIFFERENTIAL DIAGNOSIS FOR GROWTH FAILURE

The growth rate of children who are undergoing treatment for cancer typically is slow. The slow growth velocity may result from neuraxis, mantle, or total body irradiation, chemotherapy, decreased nutritional intake, increased metabolic needs, or intercurrent illness (figure 1). The growth rate usually improves or shows "catch up" after completion of therapy (figure 1). Children whose growth rate does not improve or whose growth rate is less than the mean for age and gender should be evaluated for growth failure. (See "Causes of short stature".)

Growth failure in childhood cancer survivors is caused by [1-3]: