Gigantisme & Akromegali

01Pathophysiology

Both gigantism and acromegaly are driven by chronic, autonomous oversecretion of growth hormone (GH) from a benign somatotroph adenoma in the anterior pituitary. The adenoma loses normal feedback regulation, so GH continues to be released despite negative feedback signals from IGF-1, somatostatin, and hyperglycemia. GH then acts on the liver to stimulate IGF-1 production, and IGF-1 is the primary mediator of most peripheral anabolic and growth effects. This is why IGF-1, not GH, is the most reliable circulating biomarker: GH is pulsatile and varies widely throughout the day, while IGF-1 reflects integrated 24-hour GH activity.

The clinical phenotype depends on whether the epiphyseal growth plates are still open. In children and adolescents, GH excess accelerates linear bone growth at the epiphyses, producing gigantism with abnormally tall stature. Once the epiphyses fuse at puberty, longitudinal growth stops, but periosteal and appositional bone growth, cartilage proliferation, and soft tissue overgrowth continue. This produces the acral and facial overgrowth that defines acromegaly: enlarged hands and feet, frontal bossing, prognathism, interdental spacing, macroglossia, and thickened skin.

GH directly antagonizes insulin action at the post-receptor level, producing insulin resistance, glucose intolerance, and frank diabetes mellitus in roughly a third of patients. This is a high-yield association. GH and IGF-1 also promote sodium retention and produce a hyperdynamic circulation, leading to hypertension, biventricular hypertrophy, diastolic dysfunction, and eventually a dilated cardiomyopathy, which is the leading cause of death in untreated disease.

Tumor mass effects are equally testable. A macroadenoma (>=10 mm) growing superiorly compresses the optic chiasm and produces bitemporal hemianopia. Lateral extension into the cavernous sinus can affect cranial nerves III, IV, V1, V2, and VI. Compression of normal pituitary tissue causes hypopituitarism, with secondary hypogonadism appearing earliest (amenorrhea, decreased libido, erectile dysfunction). Stalk compression can also disinhibit prolactin, producing mild hyperprolactinemia (the stalk effect), which must be distinguished from a true co-secreting adenoma.

Soft tissue overgrowth in the upper airway produces obstructive sleep apnea, and median nerve compression at the wrist produces carpal tunnel syndrome, both of which are commonly featured in vignettes. Increased epithelial proliferation also raises the risk of colonic polyps and colorectal cancer, which is why colonoscopy screening is part of routine workup.

02Classification and Clinical Manifestations

Systemic manifestations are distributed across organ systems:

03Diagnostic Workup

The workup follows a logical sequence: biochemical confirmation comes before imaging. Ordering an MRI first is a common error, because incidental pituitary microadenomas (incidentalomas) are found in roughly 10% of normal adults, and an MRI finding without biochemical confirmation can mislead.

The best initial test is serum IGF-1. GH itself is secreted in pulses and has a short half-life, so a random GH level is uninterpretable. IGF-1 has a long half-life and reflects integrated GH secretion over the preceding 24 hours. An elevated IGF-1, adjusted for age and sex, is the trigger for further testing. Note that pregnancy, late adolescence, and severe systemic illness can confound IGF-1 interpretation.

The most accurate confirmatory test is the oral glucose tolerance test. In healthy individuals, a glucose load suppresses GH below 1 ng/mL (or below 0.4 ng/mL with ultrasensitive assays). In acromegaly, the autonomous adenoma fails to suppress, and GH remains elevated or paradoxically rises. This test combines high sensitivity with the ability to demonstrate loss of normal feedback regulation, which is the physiologic essence of the disease.

Once the biochemistry is confirmed, MRI of the pituitary with contrast localizes the adenoma. Microadenomas (<10 mm) are usually fully resectable; macroadenomas (>=10 mm) raise concern for chiasmal compression and cavernous sinus invasion. If the MRI is unrevealing despite clear biochemistry, the next step is to measure serum GHRH and image the chest and abdomen to look for an ectopic GHRH-secreting neuroendocrine tumor.

Comorbidity assessment is part of the initial workup, not an afterthought. Echocardiography, sleep study, fasting glucose/HbA1c, lipid panel, and colonoscopy are routinely ordered because cardiovascular disease drives mortality and colon cancer risk is elevated.

04Management and Treatment

Transsphenoidal adenomectomy is the first-line treatment for nearly every patient, regardless of tumor size, provided the patient is a surgical candidate. Cure rates approach 85% to 90% for microadenomas and 40% to 50% for macroadenomas, with outcomes heavily dependent on the experience of the pituitary surgeon. Cure is defined biochemically as normalization of IGF-1 and a GH nadir below 1 ng/mL on oral glucose tolerance testing (or below 0.4 ng/mL with ultrasensitive assays).

When surgery does not achieve biochemical remission, or when the tumor is unresectable or invasive, medical therapy is the next step. The first-line medical agents are long-acting somatostatin receptor ligands, octreotide LAR or lanreotide depot. These bind somatostatin receptor subtype 2 on the adenoma, suppressing GH release and producing modest tumor shrinkage in roughly half of patients. Common adverse effects include gallstones, diarrhea, nausea, and worsening glucose tolerance.

Pasireotide LAR is a second-generation somatostatin ligand that binds multiple receptor subtypes and is more potent but produces hyperglycemia in a substantial portion of patients, sometimes precipitating diabetes. Cabergoline, a dopamine D2 agonist, is useful when IGF-1 elevation is mild or when the tumor co-secretes prolactin (mammosomatotroph adenoma); response is best when prolactin is elevated. Pegvisomant is a GH receptor antagonist that blocks peripheral GH action and reliably normalizes IGF-1 in over 90% of patients, but it does not suppress GH release or shrink the tumor, so MRI surveillance is required.

Radiotherapy, either stereotactic radiosurgery (Gamma Knife) or fractionated external beam, is an adjunct for residual or recurrent disease. The biochemical response takes years to develop, and the principal long-term risk is hypopituitarism, which develops in roughly half of patients within ten years.

The "Next Best Step" logic is testable in stepwise form. If a vignette describes coarsening features and enlarged hands, the next best step is to order IGF-1, not an MRI. If IGF-1 is elevated, the next best step is the oral glucose tolerance test, not imaging. If both confirm the diagnosis, the next best step is MRI of the pituitary. Once an adenoma is localized and the patient is a surgical candidate, the next best step is referral for transsphenoidal surgery.

Long-term management involves lifelong biochemical surveillance (annual IGF-1, periodic OGTT), pituitary MRI follow-up, and active treatment of comorbidities. Tight control of blood pressure, glucose, and sleep apnea normalizes the previously elevated cardiovascular mortality. Colonoscopy screening is performed at diagnosis and at intervals thereafter.

Contraindications and cautions include cabergoline in patients with significant cardiac valvulopathy at high cumulative doses (a class effect of ergot dopamine agonists), pasireotide in patients with poorly controlled diabetes, and pegvisomant monotherapy in patients with rapidly growing tumors (since it does not address the adenoma itself). In pregnancy, somatostatin ligands and pegvisomant are generally withheld unless required, and most patients can be managed conservatively because pregnancy itself often improves disease control.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common error is ordering a random GH level or going straight to pituitary MRI when acromegaly is suspected. GH is pulsatile, so a random value is uninterpretable; pituitary incidentalomas are common, so an MRI without biochemical confirmation can mislead. The correct sequence is IGF-1 first, then oral glucose tolerance test for confirmation, then MRI for localization.

The second high-yield trap is forgetting that acromegaly kills through the heart, not the head. The leading cause of death is cardiovascular disease (cardiomyopathy, hypertension, arrhythmia), not the pituitary tumor itself. Vignettes describing a long-standing acromegalic patient who develops dyspnea on exertion are testing recognition of acromegalic cardiomyopathy with diastolic dysfunction. Closely linked is obstructive sleep apnea, which is present in well over half of patients and contributes to both daytime fatigue and cardiac morbidity.

A third trap is the insidious onset and diagnostic delay. The average time from symptom onset to diagnosis is seven to ten years, and the patient's chief complaint is often not "I have acromegaly" but rather a complication: new-onset diabetes, hypertension, carpal tunnel, sleep apnea, joint pain, headache, or a change in ring or shoe size. The vignette teaches you to recognize the constellation of soft tissue overgrowth plus a metabolic complication as the pattern, not a single feature.

A fourth pearl concerns prolactin co-secretion and the stalk effect. Mildly elevated prolactin in a patient with a pituitary macroadenoma can be due to either a true co-secreting tumor or stalk compression by a non-functioning macroadenoma. The distinction matters because mammosomatotroph adenomas respond well to cabergoline, while pure somatotroph adenomas usually require somatostatin ligands.

A fifth pearl is the colorectal cancer association. Patients with acromegaly have an increased risk of colon polyps and colorectal carcinoma, so colonoscopy is part of the initial workup and is repeated periodically. Vignettes featuring an acromegalic patient with iron deficiency anemia or a positive fecal occult blood test are testing this association.

The sixth and most testable distinction is between gigantism and acromegaly, which comes down to a single anatomic fact: the state of the epiphyseal growth plates. GH excess before epiphyseal closure produces longitudinal bone growth and tall stature; GH excess after closure produces only soft tissue and appositional bone changes without increased height. A patient who develops both (rare) had GH excess that began in childhood and continued into adulthood.

Finally, recognize the next-best-step logic that examiners reward: confirm biochemically before imaging, treat surgically before medically when feasible, normalize IGF-1 as the goal of therapy, and screen aggressively for the systemic complications that determine long-term mortality. The competency being tested is recognizing a slow, multi-system clinical pattern, sequencing biochemical and imaging studies correctly, and matching treatment modality to tumor characteristics and surgical outcome.