Approach to the Patient with Endocrine Disorders¶
Chapter 388 | Part 12: Endocrinology
KEY CLINICAL POINTS¶
- Endocrine disorders require precise hormone measurement for treatment titration and homeostasis maintenance.
- Endocrine diseases are classified into hormone excess, deficiency, and resistance categories (Table 388-1).
- Genetic syndromes like MEN1/MEN2 and autoimmune conditions are major etiologic factors.
- Clinical evaluation must integrate symptoms, family history, and targeted lab/imaging.
- Management depends on disorder type: hormone replacement for deficiency, surgery/meds for excess, and addressing resistance mechanisms.
1. DEFINITION & OVERVIEW¶
Endocrinology encompasses hormone-producing glands and nonglandular hormone sources. Hormones regulate physiology via feedback mechanisms. The endocrine system interacts with the nervous, immune, and metabolic systems. Neuroendocrinology involves brain-derived hormones. Hormone receptors (GPCRs, cytokine receptors) mediate diverse physiological processes.
Table 388-1 Causes of Endocrine Dysfunction¶
| TYPE OF ENDOCRINE DISORDER | EXAMPLES |
|---|---|
| Hyperfunction | Neoplastic (Benign: Pituitary adenomas, hyperparathyroidism; Malignant: Adrenal cancer, medullary thyroid cancer; Ectopic: Ectopic ACTH, SIADH; Genetic: MEN1, MEN2; Autoimmune: Graves’ disease; Iatrogenic: Cushing’s syndrome; Infectious: Subacute thyroiditis; Activating receptor mutations: LH, TSH, Ca2+, PTH receptors, Gas) |
| Hypofunction | Autoimmune (Hashimoto’s, type 1 diabetes, Addison’s); Iatrogenic (Radiation hypopituitarism); Infectious (Adrenal insufficiency); Hormone mutations (GH, LHb, FSHb, vasopressin); Enzyme defects (21-hydroxylase); Developmental (Kallmann’s, Turner’s); Nutritional (Vitamin D, iodine); Hemorrhage (Sheehan’s) |
| Hormone Resistance | Receptor mutations (Membrane: GH, vasopressin, LH, FSH; Nuclear: AR, TR, VDR, ER, GR, PPARg); Signaling pathway mutations (Albright’s osteodystrophy); Postreceptor: Type 2 diabetes, leptin resistance |
1.1 Scope of Endocrinology¶
Traditionally focused on classical endocrine glands (pituitary, thyroid, etc.), but now includes hormones from brain, GI tract, and other organs. Hormones regulate metabolism, reproduction, growth, and homeostasis through complex feedback loops.
1.2 Hormone Action Mechanisms¶
Hormones act via membrane-bound (GPCRs) or intracellular (nuclear receptors) pathways. Receptors like GH, leptin, and steroid receptors are part of cytokine receptor families. GPCRs mediate peptide hormone actions and are involved in vision, smell, and neurotransmission.
2. EPIDEMIOLOGY¶
Endocrine disorders are common with significant population impact. Table 388-2 outlines prevalent adult disorders and screening recommendations.
Table 388-2 Prevalent Endocrine and Metabolic Disorders¶
| DISORDER | APPROXIMATE PREVALENCE IN ADULTS | SCREENING/TESTING RECOMMENDATIONS | CHAPTER(S) |
|---|---|---|---|
| Obesity | 40% Obese, BMI ‡30; 70% Overweight, BMI ‡25 | Calculate BMI; Measure waist circumference; Exclude secondary causes; Consider comorbid complications | 414 |
| Type 2 diabetes mellitus | >10% | Screen ‡45 years every 3 years; FPG >126 mg/dL; Random glucose >200 mg/dL; HbA1c elevated; Consider comorbid complications | 415 |
| Hyperlipidemia | 20–25% | Cholesterol screening every 5 years; Lipoprotein analysis (LDL, HDL); Consider secondary causes | 419 |
| Metabolic syndrome | 35% | Measure waist circumference, FPG, BP, lipids | 420 |
| Hypothyroidism | 5–10% women; 0.5–2% men | TSH; Confirm with free T4 | 396 |
| Graves’ disease | 1–3% women; 0.1% men | TSH, free T4 | 395 |
| Thyroid nodules/neoplasia | 2–5% palpable; >25% by ultrasound | Physical exam/ultrasound; Fine-needle biopsy | 397 |
| Osteoporosis | 5–10% women; 2–5% men | Bone mineral density in >65 women/postmenopausal men; Exclude secondary causes | 423 |
| Hyperparathyroidism | 0.1–0.5% women > men | Serum calcium; PTH if elevated; Assess comorbid conditions | 422 |
| Infertility | 10% couples | Investigate both partners; Semen analysis; Ovulatory cycle assessment | 403,404 |
| DISORDER | APPROXIMATE PREVALENCE IN ADULTS | SCREENING/TESTING RECOMMENDATIONS | CHAPTER(S) |
|---|---|---|---|
| Polycystic ovarian syndrome | 5–10% women | Free testosterone, DHEAS; Consider comorbid conditions | 404 |
| Hirsutism | 5–10% | Free testosterone, DHEAS; Exclude secondary causes | 406 |
| Menopause | Median age 51 | FSH measurement | 407 |
| Hyperprolactinemia | 15% women with amenorrhea/galactorrhea | PRL level; MRI if not medication-related | 392 |
| Erectile dysfunction | 10–25% | History, PRL, testosterone; Consider secondary causes (e.g., diabetes) | 409 |
| Hypogonadism (male) | 1–2% | Testosterone, LH | 403 |
| Gynecomastia | 15% | No tests often indicated; Consider Klinefelter’s, medications, liver disease | 403 |
| Klinefelter’s syndrome | 0.2% men | Karyotype; Testosterone | 402 |
| Vitamin D deficiency | 10% | Measure serum 25-OH vitamin D; Consider secondary causes | 421 |
| Turner’s syndrome | 0.03% women | Karyotype; Consider comorbid conditions | 402 |
2.1 Prevalence by Disorder¶
Obesity (40% obese, 70% overweight), type 2 diabetes (>10%), hyperlipidemia (20–25%), metabolic syndrome (35%), hypothyroidism (5–10% women), Graves’ disease (1–3% women), thyroid nodules (>25% by ultrasound), osteoporosis (5–10% women), and infertility (10% couples) are major public health concerns.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Endocrine disorders arise from hormone excess (neoplasia, autoimmune, iatrogenic), deficiency (gland destruction, genetic mutations), or resistance (receptor defects, signaling pathway issues). Genetic syndromes like MEN1/MEN2 and autoimmune conditions are key etiologic factors.
3.1 Hormone Excess Mechanisms¶
Caused by neoplasms (adenomas, carcinoids), autoimmune stimulation (Graves’ disease), or iatrogenic factors. Tumors may have defective feedback inhibition (e.g., Cushing’s disease). Activating mutations in GPCRs (LH, TSH) or G α s subunits cause premature hormone action.
3.2 Hormone Deficiency Causes¶
Gland destruction (autoimmune, infection, infarction), genetic mutations (enzyme defects, transcription factors), or iatrogenic factors (radiation, surgery). Examples include Hashimoto’s thyroiditis, Addison’s disease, and congenital hypothyroidism.
3.3 Hormone Resistance¶
Inherited defects in receptors (membrane: GH, vasopressin; nuclear: steroid receptors) or signaling pathways (Albright’s osteodystrophy). Acquired resistance occurs in type 2 diabetes, obesity, and catabolic states via receptor downregulation.
4. CLINICAL FEATURES¶
Symptoms vary by disorder type. Hormone excess presents with hyperfunction signs (e.g., Cushing’s features), while deficiency shows hypofunction symptoms (e.g., fatigue, weight gain). Hormone resistance may manifest as metabolic syndrome or end-organ dysfunction.
4.1 Hormone Excess Presentations¶
Central fat redistribution, skin striae, muscle weakness (Cushing’s); thyrotoxicosis (Graves’); parathyroid hyperplasia (hypercalcemia); tumor-related symptoms (pheochromocytoma, carcinoid syndrome).
4.2 Hormone Deficiency Signs¶
Fatigue, weight gain, cold intolerance (hypothyroidism); amenorrhea, infertility (hypogonadism); osteoporosis, adrenal insufficiency; metabolic syndrome features (obesity, glucose intolerance).
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnosis depends on disorder type. For hormone excess, consider neoplasms, autoimmune activation, or iatrogenic causes. For deficiency, evaluate gland destruction, genetic defects, or acquired factors. Hormone resistance requires assessment of receptor or signaling pathway defects.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic approach includes clinical evaluation, lab tests (hormone levels, receptor assays), and imaging (CT, MRI). Specific tests like high-dose dexamethasone suppression test for Cushing’s or genetic screening for MEN syndromes are critical.
6.1 Laboratory Tests¶
Measure hormone levels (TSH, cortisol, PTH, glucose), receptor function (e.g., GH receptor assays), and metabolic markers (lipids, HbA1c). Genetic testing for MEN syndromes or hormone receptor mutations is indicated in familial cases.
6.2 Imaging¶
CT/MRI for tumors (adrenal, pituitary, thyroid), ultrasound for thyroid nodules. Radiolabeled hormone scans may identify ectopic hormone secretion.
7. MANAGEMENT & TREATMENT¶
Treatment depends on disorder type: hormone replacement for deficiency, surgery/meds for excess, and addressing resistance mechanisms. Prophylactic interventions (e.g., thyroidectomy for MEN2) are critical in genetic syndromes.
7.1 Hormone Replacement¶
Physiologic hormone replacement for deficiencies (e.g., thyroid hormone, glucocorticoids). Monitor levels and adjust based on clinical response and lab parameters.
7.2 Surgical/Pharmacologic Interventions¶
Surgical removal of tumors (adenomas, carcinoids) or medical suppression (e.g., dopamine agonists for hyperprolactinemia). Iatrogenic excess requires discontinuation of exogenous hormones.
7.3 Resistance Management¶
Lifestyle modifications (diet, exercise) for acquired resistance (e.g., type 2 diabetes). Targeted therapies for receptor defects (e.g., leptin analogs) may be required in rare genetic cases.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis varies by disorder. Hormone excess disorders (e.g., Cushing’s) may lead to metabolic complications if untreated. Deficiency disorders (e.g., hypothyroidism) require lifelong management. Hormone resistance syndromes often have variable outcomes depending on underlying mechanisms.
8.1 Complications¶
Untreated hormone excess can cause osteoporosis, diabetes, cardiovascular disease. Deficiency may lead to infertility, metabolic syndrome, or end-organ failure. Resistance syndromes may result in progressive metabolic dysfunction.
9. SPECIAL CONSIDERATIONS¶
Pregnancy requires careful management of thyroid, adrenal, and pituitary disorders. Pediatric patients may present with growth hormone deficiency or congenital hypothyroidism. Elderly patients are at higher risk for adrenal insufficiency and osteoporosis. Genetic counseling is essential for hereditary syndromes like MEN.
10. KEY POINTS & CLINICAL PEARLS¶
- Use hormone measurements to guide treatment titration.
- Screen for endocrine disorders in high-risk populations (e.g., obesity, diabetes, family history).
- Genetic testing is critical for diagnosing hereditary syndromes (MEN, Klinefelter’s).
- Hormone resistance often requires lifestyle modifications and targeted therapies.
- Early diagnosis and intervention improve outcomes for most endocrine disorders.