Endocrinology · Pituitary Disorders
The facts most likely to be tested
Sheehan syndrome is caused by pituitary infarction secondary to postpartum hemorrhage and severe hypotension.
The primary mechanism is ischemic necrosis of the anterior pituitary gland due to its rapid expansion during pregnancy and high sensitivity to hypoperfusion.
The classic clinical presentation is the failure to lactate (agalactia) immediately following delivery due to prolactin deficiency.
Patients frequently present with secondary hypothyroidism, manifesting as fatigue, cold intolerance, and bradycardia.
Secondary adrenal insufficiency occurs due to a lack of ACTH, leading to hypoglycemia, hyponatremia, and hypotension.
Physical exam findings often include loss of axillary and pubic hair resulting from gonadotropin (LH/FSH) deficiency.
Diagnosis is confirmed by demonstrating low serum hormone levels (e.g., low TSH/T4, low ACTH/cortisol) in the setting of a history of obstetric hemorrhage.
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A 28-year-old G1P1 female presents to the clinic 3 months postpartum complaining of persistent fatigue and an inability to produce breast milk. She reports that her delivery was complicated by a severe postpartum hemorrhage requiring multiple blood transfusions. On physical exam, she has dry skin, bradycardia, and loss of axillary hair. Laboratory studies reveal low TSH, low free T4, and low morning cortisol.
What is the most likely diagnosis?
Sheehan syndrome
The patient's history of postpartum hemorrhage leading to pituitary ischemia explains the classic triad of agalactia (prolactin deficiency), secondary hypothyroidism (TSH deficiency), and secondary adrenal insufficiency (ACTH deficiency).
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High yield triage
Etiology / Epidemiology
Caused by postpartum hemorrhage leading to pituitary infarction. Occurs in patients with hypovolemic shock during delivery.
Clinical Manifestations
Failure to lactate (agalactia) is the pathognomonic sign. Look for amenorrhea and loss of axillary/pubic hair.
Diagnosis
Diagnosed via low serum hormone levels (TSH, ACTH, FSH/LH) and MRI of the pituitary showing empty sella.
Treatment
Requires lifelong hormone replacement therapy (HRT). Do not start thyroid replacement before cortisol.
Prognosis
Requires lifelong monitoring of endocrine axes. Adrenal crisis is the primary life-threatening complication.
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Epidemiology & Etiology
Sheehan syndrome is a form of panhypopituitarism resulting from ischemic necrosis of the pituitary gland. It is specifically triggered by severe postpartum hemorrhage and subsequent hypotension. The risk is highest in patients who experienced significant hypovolemic shock during childbirth.
Pertinent Anatomy
The pituitary gland undergoes hyperplasia during pregnancy, doubling in size. This expansion increases its metabolic demand and compresses the hypophyseal portal system, making it highly vulnerable to ischemic injury during systemic hypotension.
Pathophysiology
Severe blood loss leads to hypoperfusion of the pituitary gland. The resulting infarction causes a deficiency in anterior pituitary hormones, including prolactin, TSH, ACTH, and gonadotropins. Posterior pituitary function is typically preserved due to its separate blood supply.
Clinical Manifestations
The most classic presentation is the inability to lactate (agalactia) immediately postpartum. Patients may also present with amenorrhea, loss of pubic/axillary hair, and symptoms of secondary hypothyroidism or adrenal insufficiency. Adrenal crisis (hypotension, vomiting, shock) is a critical, life-threatening presentation.
Diagnosis
Diagnosis is confirmed by demonstrating low serum hormone levels (e.g., low TSH with low free T4, low ACTH with low cortisol). MRI of the pituitary is the gold standard imaging study, typically revealing an empty sella or pituitary atrophy. Stimulation tests, such as the ACTH stimulation test, may be used to assess adrenal reserve.
Treatment
Management requires lifelong hormone replacement therapy (HRT) tailored to the specific axis deficiency. Always replace glucocorticoids before thyroid hormone to prevent precipitating an adrenal crisis. Patients must be educated on increasing their glucocorticoid dose during periods of physical stress or illness.
Prognosis
Prognosis is generally good with lifelong adherence to hormone replacement. The primary risk is adrenal crisis due to missed doses or inadequate stress-dosing. Regular monitoring of serum hormone levels is required to adjust dosages.
Differential Diagnosis
Lymphocytic hypophysitis: usually presents with mass effect/headache in late pregnancy
Asherman syndrome: intrauterine adhesions causing amenorrhea without pituitary hormone deficiency
Prolactinoma: presents with galactorrhea, not agalactia
Postpartum thyroiditis: presents with transient hyper/hypothyroidism without other pituitary deficits
Simmonds disease: general term for panhypopituitarism from any cause