A breastfeeding infant, screened for congenital hypothyroidism, is found to have low levels of thyroxine (T4) and high levels of thyroid stimulating hormone (TSH). Which is the best explanation for this finding?

Hypoparathyroidism is a disorder in which the parathyroid glands produce insufficient amounts of parathyroid hormone, which regulates calcium and phosphorus levels in the body. In hypoparathyroidism, there is a decreased level of calcium in the blood, which can result in carpal spasm or tetany when pressure is applied to the upper arm.

Therefore, the nurse should review the child's calcium level (D) to determine if it is within the normal range. Low calcium levels can cause muscle spasms, seizures, and cardiac arrhythmias. Hypocalcemia may also result in other symptoms such as numbness, tingling, and muscle cramps.

Potassium (A), chloride (B), and sodium (C) are electrolytes that play important roles in various physiological processes in the body, but they are not directly related to the development of carpal spasm in a child with hypoparathyroidism. While hypokalemia (low potassium) or hyponatremia (low sodium) can cause muscle weakness or cramps, these conditions are not typically associated with carpal spasm in hypoparathyroidism.

The adolescent client's symptoms of localized pain, swelling, and tenderness, particularly at night, are suggestive of a malignancy such as osteosarcoma, which is the most common primary bone tumor in children and adolescents.

Radial ossification in the soft tissues is a characteristic finding in osteosarcoma and is indicative of bone production by malignant cells. Other imaging modalities, such as X-rays, computed tomography (CT), and magnetic resonance imaging (MRI), may also reveal osteolytic or osteoblastic lesions in the bone.

Growing pains are a common, benign condition that occur in children and do not typically present with the

symptoms described in the case scenario.

Rhabdomyolysis is a medical emergency that involves the breakdown of skeletal muscle tissue and release of muscle fiber contents into the bloodstream. It can present with muscle pain, swelling, and tenderness, but typically occurs as a result of injury, infection, or drug toxicity.

Hemosiderosis is a rare condition characterized by the accumulation of iron in various tissues, including the liver, spleen, and bone marrow. It may present with symptoms such as fatigue, joint pain, and abdominal pain, but is not typically associated with the symptoms and imaging findings described in the case scenario.

Therefore, the nurse should consider osteosarcoma as the probable cause of the adolescent client's symptoms and imaging findings, and should collaborate with the healthcare team to develop a plan of care for diagnosis and treatment.