From the Research
Hypothyroidism in Sheehan syndrome is primarily caused by the insufficient production of thyroid-stimulating hormone (TSH) due to pituitary gland necrosis resulting from severe postpartum hemorrhage and hypovolemic shock. This condition leads to secondary hypothyroidism, where the thyroid gland itself remains intact but lacks proper stimulation from the pituitary gland 1, 2. The pituitary gland's enlargement during pregnancy, without a proportional increase in blood supply, makes it vulnerable to ischemic damage when blood loss occurs, resulting in varying degrees of hypopituitarism 1.
Pathophysiology and Clinical Presentation
The pathophysiology of Sheehan syndrome involves the necrosis of the pituitary gland, which can affect the secretion of various hormones, including TSH, leading to hypothyroidism 2. The clinical presentation of Sheehan syndrome can be delayed, often becoming evident years after delivery, and includes symptoms such as failure to lactate, fatigue, and in severe cases, adrenal crisis 1.
Diagnosis and Treatment
Diagnosis is based on clinical manifestations combined with a history of severe postpartum hemorrhage, and hormone levels and/or stimulation tests can confirm the clinical suspicion 1. Treatment involves hormone replacement therapy, with thyroid hormone replacement being a critical component for managing hypothyroidism 1, 2. It is essential to carefully manage the dosing of levothyroxine, typically starting at 1.6 mcg/kg/day, and to prioritize cortisol replacement before thyroid replacement to avoid precipitating an adrenal crisis 2. Regular monitoring of free T4 levels, rather than TSH, is necessary to guide treatment, as TSH levels can be inappropriately low due to pituitary damage 3.
Recent Findings
Recent studies have highlighted the importance of understanding the bioactivity of TSH in Sheehan's syndrome, showing that despite elevated immunoreactive TSH levels, the bioactive TSH concentrations may not be significantly different from control values due to decreased intrinsic TSH bioactivity 3. This finding supports the need for careful management of thyroid hormone replacement therapy in these patients.
Management Priorities
The management of hypothyroidism in Sheehan syndrome should prioritize the replacement of deficient hormones, careful dosing of levothyroxine, and regular monitoring of free T4 levels. Given the potential for multiple pituitary hormone deficiencies, a comprehensive approach to hormone replacement therapy is essential to improve the quality of life and reduce morbidity and mortality in patients with Sheehan syndrome 1, 2.