USMLE Guide: Pituitary Disorders

Introduction

This guide will provide an overview of pituitary disorders, which are common topics on the United States Medical Licensing Examination (USMLE). Pituitary disorders involve dysfunctions in the pituitary gland, a small gland located at the base of the brain. Familiarity with pituitary disorders is essential for medical professionals, as they can have significant clinical implications. This guide will cover the key concepts, pathophysiology, clinical presentations, diagnostic approaches, and treatment options for pituitary disorders.

Table of Contents

1. Anatomy and Physiology of the Pituitary Gland
2. Overview of Pituitary Disorders
3. Acromegaly
4. Cushing's Disease
5. Prolactinoma
6. Diabetes Insipidus
7. Hypopituitarism
8. Diagnostic Approaches
9. Treatment Options

1. Anatomy and Physiology of the Pituitary Gland

The pituitary gland consists of two main lobes: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). The anterior pituitary is responsible for producing and releasing various hormones, including growth hormone, adrenocorticotropic hormone, thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, and prolactin. The posterior pituitary stores and releases antidiuretic hormone (ADH) and oxytocin, which are produced in the hypothalamus.

2. Overview of Pituitary Disorders

Pituitary disorders can be broadly categorized into hyperfunctioning (excess hormone production) or hypofunctioning (insufficient hormone production) conditions. Common pituitary disorders include acromegaly, Cushing's disease, prolactinoma, diabetes insipidus, and hypopituitarism.

3. Acromegaly

Acromegaly is a rare disorder caused by excessive growth hormone production, usually due to a pituitary adenoma. It primarily affects adults and leads to the enlargement of bones and tissues, particularly in the extremities. Clinical features may include enlarged hands and feet, facial changes, joint pain, and organomegaly. Diagnosis is based on elevated insulin-like growth factor-1 (IGF-1) levels and confirmatory oral glucose tolerance test. Treatment involves surgical resection of the pituitary tumor, radiation therapy, or medical therapy with somatostatin analogs.

4. Cushing's Disease

Cushing's disease refers to the hypersecretion of adrenocorticotropic hormone (ACTH) from a pituitary adenoma. This excess ACTH stimulates the adrenal glands to produce excess cortisol, resulting in a variety of clinical manifestations such as central obesity, moon facies, buffalo hump, thin skin, muscle weakness, and hypertension. Diagnosis involves measuring 24-hour urinary free cortisol levels, late-night salivary cortisol levels, and performing a low-dose dexamethasone suppression test. Surgical resection of the pituitary tumor is the primary treatment, while medical therapy and radiation therapy may be used as adjuncts.

5. Prolactinoma

Prolactinomas are benign pituitary tumors that secrete excessive prolactin. They are the most common functional pituitary adenomas. Elevated prolactin levels can lead to amenorrhea, galactorrhea, and infertility in women, and erectile dysfunction and gynecomastia in men. Diagnosis is based on elevated serum prolactin levels and imaging studies such as magnetic resonance imaging (MRI). Treatment options include dopamine agonists, such as bromocriptine or cabergoline, which reduce prolactin secretion and tumor size.

6. Diabetes Insipidus

Diabetes insipidus is a disorder characterized by the inability to concentrate urine due to insufficient production or action of ADH (vasopressin). This condition can be caused by either central (lack of ADH production) or nephrogenic (resistance to ADH) factors. Patients present with polyuria, polydipsia, and nocturia. Diagnosis involves water deprivation tests and measurement of urine osmolality. Treatment depends on the underlying cause and may involve desmopressin (synthetic ADH) administration or addressing the underlying condition.

7. Hypopituitarism

Hypopituitarism refers to the inadequate secretion of one or more pituitary hormones. Causes include pituitary tumors, pituitary apoplexy, trauma, or Sheehan syndrome (postpartum pituitary necrosis). Clinical presentations depend on the specific hormones affected. Common manifestations include fatigue, weight loss, hypotension, amenorr