Approach to the Patient with Endocrine Disorders¶
Chapter 388 | Part 12: Endocrinology and Metabolism · Part 12 – Endocrinology & Metabolism · Chapter 388
Key Clinical Points¶
- Endocrine disorders are classified into three major types: hormone excess, hormone deficiency, and hormone resistance.
- Most endocrine disorders are amenable to effective treatment once correct diagnosis is established.
- Hormone deficiency is treated with physiologic hormone replacement; hormone excess is managed by tumor removal or medical therapy.
- Clinical evaluation focuses on manifestations of hormone excess/deficiency and direct examination of palpable glands.
- Laboratory testing allows quantitative assessment of hormone levels and dynamics.
- Radiologic imaging (CT, MRI) is essential for localization and characterization of endocrine tumors.
- MEN1 is characterized by a triad of parathyroid, pancreatic islet, and pituitary tumors (menin tumor-suppressor gene).
- MEN2 is caused by activating mutations in the RET protooncogene (receptor tyrosine kinase).
- Autoimmune endocrine diseases are caused by dysregulation of immune surveillance and tolerance.
- Functional hormone resistance involves receptor downregulation and postreceptor desensitization (generally reversible).
DEFINITION & OVERVIEW¶
• Definition: Endocrinology encompasses the study of glands and hormones they produce, including those from the brain, GI tract, musculoskeletal system, and other nonglandular organs. • Core Concept: The term endocrine (contrasted with exocrine) refers to internally secreted hormones. Endocrine systems are not defined strictly by anatomy; they communicate via the nervous system, hormones, cytokines, and growth factors. • Hormone Action & Feedback Control: ◦ Assessment: Primarily measured via hormone concentrations. ◦ Management requires understanding of intermediary metabolism, reproductive physiology, bone metabolism, and growth. ◦ Treatment Logic: ◦ Deficiency → Physiologic hormone replacement. ◦ Excess → Surgical tumor removal or medical reduction of levels. • Scope of Endocrinology: ◦ Core glands: Pituitary, thyroid, parathyroid, pancreatic islets, adrenals, and gonads. ◦ Neuroendocrinology: Brain produces peptide hormones; CNS influences pituitary via releasing factors. ◦ Peripheral Nervous System: Stimulates the adrenal medulla. ◦ Immune-Endocrine Link: Cortisol is a potent immunosuppressant. Cytokines and interleukins (ILs) have profound effects on pituitary, adrenal, thyroid, and gonads. Common diseases (e.g., autoimmune thyroid disease, type 1 diabetes) result from dysregulation of immune surveillance. • Hormone Sources & Functions: ◦ Kidney: Source of atrial natriuretic peptide; produces erythropoietin; involved in renin-angiotensin axis. Target for PTH, mineralocorticoids, FGF23, and vasopressin. ◦ GI Tract: Produces GLP1, cystokinin, ghrelin, gastrin, secretin, and vasoactive intestinal peptide. ◦ Adipose Tissue: Produces leptin (central appetite control), adiponectin, and resistin. • Receptor Biology: ◦ Cytokine Family: Growth hormone (GH) and leptin receptors belong to this family. ◦ G Protein-Coupled Receptors (GPCRs): Mediate actions of peptide hormones in vision, smell, and neurotransmission. ◦ Genetic Mutations: ◦ LH receptor mutation → dominantly transmitted male-limited precocious puberty (premature testosterone synthesis in Leydig cells). ◦ Gα mutations → McCune-Albright syndrome (early) or GH-secreting tumors and acromegaly (somatropes). ◦ Autoimmunity: In Graves' disease, antibodies mimic TSH action by inducing conformational changes in the TSH receptor, triggering coupling to G proteins.
EPIDEMIOLOGY¶
• Prevalence Overview: Varies among ethnic groups and with aging; data primarily based on U.S. population. • Common Conditions (Table 388-2): ◦ Obesity: 40% Obese (BMI ≥30), 70% Overweight (BMI ≥25). ◦ Type 2 Diabetes Mellitus: >10%. ◦ Hyperlipidemia: 20–25%. ◦ Metabolic Syndrome: 35%. ◦ Hypothyroidism: 5–10% women, 0.5–2% men. ◦ Graves' Disease: 1–3% women, 0.1% men. ◦ Thyroid Nodules and Neoplasia: 2–5% palpable, >25% by ultrasound. ◦ Osteoporosis: 5–10% women, 2–5% men. ◦ Hyperparathyroidism: 0.1–0.5% women > men. ◦ Infertility: 10% of couples. ◦ Polycystic Ovarian Syndrome (PCOS): 5–10% women. ◦ Hirsutism: 5–10%. ◦ Menopause: Median age, 51. ◦ Hyperprolactinemia: 15% in women with amenorrhea or galactorrhea. ◦ Erectile Dysfunction: 10–25%. ◦ Hypogonadism (male): 1–2%. ◦ Gynecomastia: 15%. ◦ Klinefelter's Syndrome: 0.2% men. ◦ Turner's Syndrome: 0.03% women. ◦ Vitamin D Deficiency: 10%.
ETIOLOGY & PATHOPHYSIOLOGY¶
• Hormone Excess (Table 388-1): ◦ Neoplastic: ◦ Benign: Pituitary adenomas, hyperparathyroidism, autonomous thyroid or adrenal nodules. ◦ Malignant: Adrenal cancer, medullary thyroid cancer, carcinoid. ◦ Ectopic: Ectopic ACTH, SIADH secretion. ◦ Genetic Predisposition: MEN1, MEN2. ◦ Autoimmune: Graves' disease. ◦ Iatrogenic: Cushing's syndrome, hypoglycemia. ◦ Infectious/Inflammatory: Subacute thyroiditis. ◦ Activating Receptor Mutations: LH, TSH, Ca2+, PTH receptors, Gαs. • Hormone Deficiency (Table 388-1): ◦ Autoimmune: Hashimoto's thyroiditis, type 1 diabetes mellitus, Addison's disease, polyglandular failure. ◦ Iatrogenic: Radiation-induced hypopituitarism, hypothyroidism, surgical. ◦ Infectious/Inflammatory: Adrenal insufficiency, hypothalamic sarcoidosis. ◦ Hormone Mutations: GH, LHβ, FSHβ, vasopressin. ◦ Enzyme Defects: 21-Hydroxylase deficiency. ◦ Developmental Defects: Kallmann's syndrome, Turner's syndrome, transcription factors. ◦ Nutritional/Vitamin Deficiency: Vitamin D deficiency, iodine deficiency. ◦ Hemorrhage/Infarction: Sheehan's syndrome, adrenal insufficiency. • Hormone Resistance (Table 388-1): ◦ Membrane Receptor Mutations: GH, vasopressin, LH, FSH, ACTH, GnRH, GHRH, PTH, leptin, Ca2+. ◦ Nuclear Receptor Mutations: AR, TR, VDR, ER, GR, PPARγ. ◦ Signaling Pathway Mutations: Albright's hereditary osteodystrophy. ◦ Postreceptor (Functional): Type 2 diabetes mellitus, leptin resistance. • MEN Syndromes: ◦ MEN1: Triad of parathyroid, pancreatic islet, and pituitary tumors; caused by mutation in menin gene (11q13). ◦ MEN2: Medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism; caused by activating mutations in RET protooncene. • Pathophysiology of Hormone Excess: ◦ Benign endocrine tumors often retain capacity to produce hormones because they are relatively well differentiated. ◦ Many endocrine tumors exhibit subtle defects in their set points for feedback regulation.
CLINICAL FEATURES¶
• Clinical Evaluation Principles: ◦ Focus on manifestations of hormone excess/deficiency. ◦ Direct examination of palpable glands (thyroid, gonads). ◦ Clinical judgment is required to distinguish non-specific findings (e.g., obesity, hypertension) from specific endocrine manifestations.
DIFFERENTIAL DIAGNOSIS¶
• Distinguishing Features: ◦ Distinguish between common/non-specific findings (e.g., obesity, hypertension) and specific endocrine manifestations that require investigation.
INVESTIGATIONS & DIAGNOSIS¶
- Laboratory Testing: ◦ Purpose: Quantitative assessment of hormone levels and dynamics. ◦ Timing: Early testing indicated in patients with symptoms or those at increased risk. ◦ Specific Tests (Table 388-2): ◦ Obesity → BMI, waist circumference. ◦ T2DM → FPG (>126 mg/dL), Random plasma glucose (>200 mg/dL), HbA1c. ◦ Hypothyroidism → TSH, free T4. ◦ Hyperparathyroidism → Serum calcium, PTH (if calcium is elevated). ◦ Other conditions: Follow specific protocols as indicated in respective chapters.
- Radiologic Imaging: ◦ Modalities: CT, MRI. ◦ Purpose: Essential for localization and characterization of endocrine tumors.
Imaging Utility¶
• Localization: Identifying the site of a tumor. ◦ Characterization: Determining the nature/type of the tumor.
MANAGEMENT & TREATMENT¶
- General Management Principles: ◦ Diagnosis → Treatment (most endocrine disorders are amenable to treatment once diagnosed).
- Treatment by Pathology Type: ◦ Hormone Deficiency → Physiologic hormone replacement. ◦ Hormone Excess → Surgical tumor removal or medical reduction of hormone levels.
- Precision Medicine in Endocrinology: ◦ Use precise measurements to titrate treatment regimens and maintain/restore homeostasis.
Treatment Response¶
• Assessment: Criteria vary by specific disorder; assessment of response is critical for ongoing management.
PROGNOSIS & COMPLICATIONS¶
• Treatment Response: ◦ Success depends on the timing of diagnosis and the extent of glandular damage.
SPECIAL CONSIDERATIONS¶
• Demographic Variations: ◦ Prevalence varies among ethnic groups and with aging. ◦ Data primarily based on U.S. population.
KEY PEARLS & CLINICAL TRAPS¶
• Clinical Pearls: ◦ Treatment Logic: Deficiency = Replacement; Excess = Surgery/Medical reduction. ◦ MEN Distinction: MEN1 (Menin, 11q13) vs. MEN2 (RET protooncene). ◦ Imaging Role: CT and MRI are the primary modalities for tumor localization and characterization. • Clinical Traps: ◦ Distinguishing specific endocrine signs from non-specific findings (e.g., obesity, hypertension) is critical for determining the necessity of extensive workup.
Reference Tables¶
TABLE 388-1 Causes of Endocrine Dysfunction¶
Harrison's 22e, p.2978
| TYPE OF ENDOCRINE DISORDER | EXAMPLES |
|---|---|
| Hyperfunction | |
| Neoplastic Benign Malignant Ectopic Genetic predisposition Autoimmune Iatrogenic Infectious/inflammatory Activating receptor mutations |
Pituitary adenomas, hyperparathyroidism, autonomous thyroid or adrenal nodules Adrenal cancer, medullary thyroid cancer, carcinoid Ectopic ACTH, SIADH secretion MEN1, MEN2 Graves’ disease Cushing’s syndrome, hypoglycemia Subacute thyroiditis LH, TSH, Ca2+, PTH receptors, Gα s |
| Hypofunction | |
| Hormone Resistance | |
| Receptor mutations Membrane Nuclear Signaling pathway mutations Postreceptor |
GH, vasopressin, LH, FSH, ACTH, GnRH, GHRH, PTH, leptin, Ca2+ AR, TR, VDR, ER, GR, PPARγ Albright’s hereditary osteodystrophy Type 2 diabetes mellitus, leptin resistance |
TABLE 388-2 Examples of Prevalent Endocrine and Metabolic Disorders in the Adult DISORDER Obesity¶
Harrison's 22e, p.2979
| DISORDER | APPROXIMATE PREVALENCE IN ADULTSa | SCREENING/TESTING RECOMMENDATIONSb | CHAPTER(S) |
|---|---|---|---|
| Obesity | 40% Obese, BMI ≥30 70% Overweight, BMI ≥25 |
Calculate BMI Measure waist circumference Exclude secondary causes Consider comorbid complications |
414 |
| >10% | Beginning at age 45, screen every 3 years, or earlier in high-risk groups: FPG >126 mg/dL Random plasma glucose >200 mg/dL An elevated HbA 1c Consider comorbid complications |
||
| Hyperlipidemia | 20–25% | Cholesterol screening at least every 5 years; more often in high-risk groups Lipoprotein analysis (LDL, HDL) for increased cholesterol, CAD, diabetes Consider secondary causes |
419 |
| 35% | Measure waist circumference, FPG, BP, lipids | ||
| Hypothyroidism | 5–10%, women 0.5–2%, men |
TSH; confirm with free T 4 |
396 |
| 1–3%, women 0.1%, men |
TSH, free T 4 |
||
| Thyroid nodules and neoplasia | 2–5% palpable >25% by ultrasound |
Physical examination or ultrasound of thyroid Fine-needle aspiration biopsy |
397 |
| 5–10%, women 2–5%, men |
Bone mineral density measurements in women >65 years or in postmenopausal women or men at risk Exclude secondary causes |
||
| Hyperparathyroidism | 0.1–0.5%, women > men | Serum calcium PTH, if calcium is elevated Assess comorbid conditions |
422 |
| 10%, couples | Investigate both members of couple Semen analysis in male Assess ovulatory cycles in female Specific tests as indicated |
||
| Polycystic ovarian syndrome | 5–10%, women | Free testosterone, DHEAS Consider comorbid conditions |
404 |
| 5–10% | Free testosterone, DHEAS Exclude secondary causes Additional tests as indicated |
||
| Menopause | Median age, 51 | FSH | 407 |
| 15% in women with amenorrhea or galactorrhea |
PRL level MRI, if not medication-related |
||
| Erectile dysfunction | 10–25% | Careful history, PRL, testosterone Consider secondary causes (e.g., diabetes) |
409 |
| 1–2% | Testosterone, LH | ||
| Gynecomastia | 15% | Often, no tests are indicated Consider Klinefelter’s syndrome Consider medications, hypogonadism, liver disease |
403 |
| 0.2%, men | Karyotype Testosterone |
||
| Vitamin D deficiency | 10% | Measure serum 25-OH vitamin D Consider secondary causes |
421 |
| 0.03%, women | Karyotype Consider comorbid conditions |