AM Report 1/23/17: Endocrinology Board Review

Surreptitious Insulin Use:
– Exogenous insulin intake is associated with increased insulin and low C-peptide levels

Whipple’s Triad:
1.Symptoms consistent with hypoglycemia
2.Documented low plasma glucose when symptoms are present
3.Relief of symptoms following resolution of hypoglycemia

– Consider a psychiatric evaluation in patient’s suspected of intentional exogenous insulin use

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– Endogenous insulin is formed as two insulin chains (A&B) linked by C-peptide.  Measurement of C-peptide can help distinguish from endogenous versus exogenous insulin

Insulinoma:
Diagnosis:
– Clinical + measurement of insulin (normal or elevated), proinsulin (normal or elevated), and C-peptide (normal or elevated)
– Localization of tumor with imaging; start with CT of the abdomen

Glucose Insulin Proinsulin C-peptide BHB
Exogenous Insulin
Insulinoma, NIPHS, PGHS ↑/NL ↑/NL ↑/NL
Sulfonylurea Ingestion

– Use a urine sulfonylurea toxicity screen to distinguish insulinoma from sulfonylurea ingestion

Pheochromocytoma:

– always think about pheo when the clinical case includes episodes of hypertension and headache

– Pheochromocytomas are tumors composed of chromaffin cells of the adrenal gland

– Pheochromocytomas almost always realease catecholamines

Classic Triad:

– Diaphoresis

– Headache

– Tachycardia

Genetic disorder associated with pheochromocytoma:

– MEN 2A and 2B

– Neurofibromatosis type 1

– Von Hippel-Lindau syndrome

Diagnosis: – Plasma / Urine catecholamines

– plasma high sensitivity (96-100%), but lower specificity (85-89%); 24 hour urine sensitivity/specificity (91-98%)

– Plasma will exclude a pheo when negative, but need to confirm if positive

– Following biochemical diagnosis – radiographic localization is needed

Preoperative management:

– Alpha-blocker – typically with phenoxybenzamine – is first-line therapy; followed by B-blockers (metoprolol, propranolol) to treat reflex tachycardia

MEN 1, 2A, and 2B disorders:

MEN 1: Pituitary adenoma, Parathyroid hyperplasia, Pancreatic tumors

MEN 2A: Medullary thyroid cancer, Parathyroid hyperplasia, Pheochromcytoma

MEN 2B: Medullary thyroid cancer, Marfanoid habitus/Mucosal neuroma, Pheochromocytoma

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Cushing Syndrome:
– Bright purple abdominal striae always, always, always are associated with Cushing syndrome – striae larger than 1 cm in width are highly specific for hypercortisolism
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Other classic stigmata:
– cervicodorsal fat pad aka “buffalo hump,” acne, hirsutism, moon facies, plethora, easy bruising, hypertension, insulin resistance, hypokalemic metabolic alkalosis, osteoporosis

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Cause:
– Elevated cortisol
– Most common cause is exogenous glucocorticoid therapy for another cause

3 biochemical testing options for CS:
– 1 mg (low dose) dexamethasone suppression test – failure to suppress AM cortisol indicates true Cushing syndrome
– 24 hour urine free cortisol (UFC) – excludes CS when not elevated
– Late-night salivary cortisol
Never measure a random cortisol as part of the work up

After confirming CS biochemically, measure ACTH to establish etiology
– differentiate between ACTH-dependent/Cushing Disease (usually > 20 pg/mL) and ACTH-independent (usually < 5 pg/mL)

If ACTH-dependent CS: order pituitary MRI
If ACTH-independent CS: adrenal gland imaging (either CT or MRI)

ACTH-secreting pituitary adenoma is known as Cushing disease
Pearl: pituitary adenomas do not suppress with low-dose dex, but do suppress with high dose

Other possible ACTH-secreting tumors (but very rare):
– An ectopic ACTH-secreting tumor
– Usually these are primary lung cancers or a carcinoid tumor
– The clinical presentation of an ectopic lung tumor usually is less cushingoid (presenting with only HTN and metabolic abnormalities) due to the rapid growth of these tumors


			

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