# Clinical Cases: Endocrine Principles ## Case 1: Cushing Syndrome - Cortisol Excess and Feedback Dysregulation ### Clinical Image ![Cushing Syndrome](case_01_image.jpg) *Source: [Wikimedia Commons - Cushing syndrome](https://commons.wikimedia.org/wiki/File:Cushing%27s_syndrome.jpg) - CC BY-SA 4.0* ### Patient Presentation A 42-year-old woman presents to her primary care physician with a 6-month history of progressive weight gain, particularly around her abdomen and face, despite no change in diet or activity. She also notes easy bruising, irregular menstrual periods, and new-onset difficulty climbing stairs. Her husband has noticed that she seems more irritable and has been having trouble sleeping. ### Demographics - Age: 42 years - Sex: Female - Past Medical History: Hypertension (newly diagnosed 4 months ago), Type 2 diabetes (diagnosed 2 months ago) ### Chief Complaint Progressive central weight gain, easy bruising, and proximal muscle weakness ### Physical Examination - Blood pressure: 158/96 mmHg - Heart rate: 82 bpm - BMI: 32 kg/m2 - General: Moon facies, facial plethora, dorsocervical fat pad ("buffalo hump") - Skin: Thin skin with multiple ecchymoses, wide (>1 cm) violaceous striae on abdomen - Musculoskeletal: Proximal muscle weakness (difficulty rising from chair) - Extremities: Thin arms and legs relative to trunk ### Workup - 24-hour urine free cortisol: 485 mcg/day (elevated; normal <50 mcg/day) - Late-night salivary cortisol: Elevated on two occasions - Low-dose dexamethasone suppression test: Cortisol 18 mcg/dL (failed suppression; normal <1.8 mcg/dL) - ACTH level: 68 pg/mL (elevated; suggests ACTH-dependent Cushing syndrome) - High-dose dexamethasone suppression test: >50% suppression (suggests pituitary source) - Pituitary MRI: 6 mm microadenoma in right anterior pituitary ### Diagnosis Cushing Disease (ACTH-secreting pituitary adenoma) ### Treatment 1. Transsphenoidal surgical resection of pituitary adenoma 2. Perioperative stress-dose glucocorticoids 3. Postoperative monitoring for adrenal insufficiency 4. Management of comorbidities (hypertension, diabetes) 5. Long-term follow-up for recurrence ### Physiological Principles Demonstrated - **Negative feedback failure**: The pituitary adenoma secretes ACTH autonomously, not responding to elevated cortisol levels. This demonstrates failure of the normal long-loop negative feedback mechanism where cortisol should suppress CRH and ACTH. - **Hormone excess effects**: Chronic cortisol excess produces the classic phenotype through multiple mechanisms: protein catabolism (muscle weakness, thin skin), altered fat distribution (central obesity, moon facies), hyperglycemia (diabetes), and hypertension. - **Hypothalamic-pituitary-adrenal axis**: This case illustrates the HPA axis hierarchy, where ACTH from the pituitary controls cortisol release from the adrenal cortex. - **Dynamic testing**: The dexamethasone suppression tests exploit the feedback system to differentiate causes of hypercortisolism. --- ## Case 2: Primary Hypothyroidism - Interpreting Hormone Levels with Feedback ### Clinical Image ![Thyroid Goiter](case_02_image.jpg) *Source: [Wikimedia Commons - Goiter](https://commons.wikimedia.org/wiki/File:Struma_001.jpg) - CC BY-SA 3.0* ### Patient Presentation A 35-year-old woman presents with a 4-month history of fatigue, weight gain of 15 pounds, constipation, and feeling cold all the time. She also reports dry skin, hair loss, and difficulty concentrating at work. Her menstrual periods have become heavier and more frequent. ### Demographics - Age: 35 years - Sex: Female - Past Medical History: None significant - Family History: Mother with "thyroid problems" ### Chief Complaint Fatigue, weight gain, cold intolerance, and constipation ### Physical Examination - Blood pressure: 108/72 mmHg - Heart rate: 56 bpm (bradycardic) - Temperature: 36.2°C (low normal) - General: Appears fatigued, mild periorbital puffiness - Thyroid: Diffusely enlarged, firm, non-tender - Skin: Cool, dry skin; brittle nails - Reflexes: Delayed relaxation phase (hung-up reflexes) ### Workup - TSH: 48 mIU/L (markedly elevated; normal 0.4-4.0 mIU/L) - Free T4: 0.4 ng/dL (low; normal 0.8-1.8 ng/dL) - Anti-TPO antibodies: Positive (elevated titer) - Anti-thyroglobulin antibodies: Positive - Lipid panel: Total cholesterol 268 mg/dL, LDL 172 mg/dL (elevated) ### Diagnosis Primary Hypothyroidism due to Hashimoto's Thyroiditis ### Treatment 1. Levothyroxine replacement therapy (starting dose 1.6 mcg/kg/day) 2. Recheck TSH in 6-8 weeks and titrate dose 3. Goal: Normalize TSH 4. Education about lifelong therapy and medication interactions 5. Screen for other autoimmune conditions ### Physiological Principles Demonstrated - **Primary vs. secondary endocrine disorders**: The pattern of low T4 with elevated TSH indicates the problem is at the thyroid gland (primary), not the pituitary. Intact negative feedback causes TSH to rise in response to low thyroid hormone. - **Negative feedback in action**: The elevated TSH demonstrates the pituitary's appropriate response to low circulating thyroid hormone - the feedback loop is intact but the thyroid cannot respond. - **Thyroid hormone effects**: The clinical features reflect decreased metabolic rate throughout the body: bradycardia, cold intolerance, constipation, weight gain, and mental slowing. - **Autoimmune pathophysiology**: TPO antibodies indicate autoimmune destruction of the thyroid gland, a common cause of primary hypothyroidism. --- ## Case 3: Pheochromocytoma - Catecholamine Excess ### Clinical Image ![Pheochromocytoma CT](case_01_image.jpg) *Source: [Radiopaedia - Pheochromocytoma](https://radiopaedia.org/cases/pheochromocytoma) - Used for educational purposes* ### Patient Presentation A 38-year-old man is brought to the emergency department after experiencing an episode of severe headache, profuse sweating, palpitations, and anxiety that lasted about 30 minutes. He describes similar episodes occurring 2-3 times per week over the past 3 months. During these episodes, his wife notes that he becomes pale and tremulous. Between episodes, he feels relatively normal. ### Demographics - Age: 38 years - Sex: Male - Past Medical History: Hypertension (diagnosed 1 year ago, difficult to control) - Medications: Three antihypertensive medications ### Chief Complaint Episodic headaches, palpitations, sweating, and anxiety ### Physical Examination (during episode) - Blood pressure: 228/124 mmHg - Heart rate: 118 bpm - Temperature: 37.8°C - General: Anxious, diaphoretic, pallor - Cardiovascular: Tachycardic, regular rhythm, no murmurs - Pupils: Dilated ### Workup - 24-hour urine metanephrines: Markedly elevated - 24-hour urine catecholamines: Epinephrine and norepinephrine elevated - Plasma free metanephrines: Elevated - CT abdomen: 4 cm heterogeneous mass in the right adrenal gland - MIBG scan: Intense uptake in right adrenal mass ### Diagnosis Pheochromocytoma (catecholamine-secreting adrenal tumor) ### Treatment 1. Alpha-blockade (phenoxybenzamine) initiated first - 10-14 days preoperatively 2. Beta-blockade added only AFTER adequate alpha-blockade 3. Liberal salt and fluid intake to expand volume 4. Surgical adrenalectomy (laparoscopic) 5. Intraoperative monitoring for hemodynamic instability 6. Genetic testing for hereditary syndromes (MEN2, VHL, SDH mutations) ### Physiological Principles Demonstrated - **Catecholamine receptor mechanisms**: Episodic release of catecholamines produces classic symptoms through alpha and beta receptor activation: vasoconstriction (hypertension, pallor), cardiac stimulation (tachycardia, palpitations), sweating, and metabolic effects. - **G-protein coupled receptor signaling**: Catecholamines act through GPCRs to activate adenylyl cyclase (beta receptors) or phospholipase C (alpha-1 receptors), producing rapid physiological effects. - **Treatment sequence rationale**: Alpha-blockade must precede beta-blockade because blocking beta-mediated vasodilation without first blocking alpha-mediated vasoconstriction can cause unopposed alpha effects and hypertensive crisis. - **Hormone measurement**: Metabolites (metanephrines) are more stable than catecholamines themselves and provide better diagnostic sensitivity.