USMLE Guide: Endocrine Disorders

Introduction

Endocrine disorders are a group of medical conditions that result from dysfunction or abnormality in the endocrine system. This system consists of various glands throughout the body that produce and secrete hormones, which are essential for regulating bodily functions. Understanding the key concepts and clinical manifestations of endocrine disorders is crucial for medical students preparing for the USMLE exams. This guide aims to provide a concise overview of important endocrine disorders, their pathophysiology, clinical features, diagnostic approaches, and treatment options.

Table of Contents

1. Hypothyroidism
2. Hyperthyroidism
3. Diabetes Mellitus
4. Cushing's Syndrome
5. Addison's Disease
6. Hyperparathyroidism
7. Hypoparathyroidism
8. Pheochromocytoma
9. Acromegaly
10. Polycystic Ovary Syndrome (PCOS)

Hypothyroidism

Pathophysiology

Hypothyroidism is characterized by decreased thyroid hormone production. The most common cause is Hashimoto's thyroiditis, an autoimmune disorder leading to destruction of thyroid tissue. Other causes include iodine deficiency, medications, and certain genetic conditions.

Clinical Features

• Fatigue, weight gain, and cold intolerance
• Bradycardia, constipation, and dry skin
• Myxedema (severe hypothyroidism): facial and periorbital edema, non-pitting edema of hands and feet, and coarse hair

Diagnosis

• Elevated thyroid-stimulating hormone (TSH) and low free thyroxine (T4) levels
• Anti-thyroid peroxidase (TPO) antibodies may be positive in autoimmune cases

Treatment

• Levothyroxine replacement therapy

Hyperthyroidism

Pathophysiology

Hyperthyroidism is characterized by excessive production of thyroid hormones. The most common cause is Graves' disease, an autoimmune disorder resulting in overstimulation of the thyroid gland. Other causes include toxic multinodular goiter and toxic adenoma.

Clinical Features

• Heat intolerance, weight loss, and palpitations
• Tremor, diarrhea, and increased appetite
• Thyroid eye disease (Graves' ophthalmopathy): proptosis, lid lag, and extraocular muscle dysfunction

Diagnosis

• Low TSH and elevated free T4 levels
• Positive thyroid-stimulating immunoglobulin (TSI) in Graves' disease

Treatment

• Anti-thyroid medications (e.g., methimazole)
• Radioactive iodine therapy
• Surgical thyroidectomy (in certain cases)

diabetes mellitus

Pathophysiology

Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia. Type 1 diabetes is due to autoimmune destruction of pancreatic beta cells, while type 2 diabetes involves insulin resistance and impaired insulin secretion.

Clinical Features

• Polyuria, polydipsia, and unexplained weight loss
• Blurred vision, fatigue, and recurrent infections
• Diabetic ketoacidosis (in type 1 diabetes): fruity breath, abdominal pain, and rapid breathing

Diagnosis

• Fasting plasma glucose ≥126 mg/dL or random plasma glucose ≥200 mg/dL (in the presence of symptoms)
• HbA1c ≥6.5% (reflects average blood glucose over the past 2-3 months)

Treatment

• Type 1 diabetes: insulin replacement therapy
• Type 2 diabetes: lifestyle modifications (diet, exercise) and oral antidiabetic medications (e.g., metformin)

cushing's syndrome

Pathophysiology

Cushing's syndrome results from chronic exposure to excessive glucocorticoids, either exogenous or endogenous. The most common cause is exogenous administration of glucocorticoids for various medical conditions. Endogenous causes include adrenal adenoma or carcinoma, pituitary adenoma (Cushing's disease), or ectopic adrenocorticotropic hormone (ACTH) production.

Clinical Features

• Central obesity, moon facies, and buffalo hump
• Proximal muscle weakness and thin