TABLE IV-114 Risk Factors for Active Tuberculosis Among Persons Who Have Been Infected With Tubercle Bacilli 31 page

A. A patient with a bone density less than the mean of age-, race-, and gender-matched controls

B. A patient with a bone density less than 1.0 standard deviation (SD) below the mean of race- and
gender-matched controls

C. A patient with a bone density less than 1.0 SD below the mean of age-, race-, and gender-
matched controls

D. A patient with a bone density less than 2.5 SD below the mean of race- and gender-matched
controls

E. A patient with a bone density less than 2.5 SD below the mean of age-, race-, and gender-
matched controls

X-90. A 66-year-old Asian woman seeks treatment for osteoporosis. She fell and fractured her right hip, requiring a surgical intervention 3 months ago. She was told while hospitalized that she had osteoporosis but had not previously been evaluated for this. During the hospitalization, she developed a deep venous thrombosis (DVT) with pulmonary embolus, for which she is currently taking warfarin. She completed menopause at age 52. She is a former smoker, quitting about 6 years ago. She has always been thin, and her current body mass index (BMI) is 19.2 kg/m². Her laboratory studies show calcium of 8.7 mg/dL, phosphate of 3 mg/dL, creatinine of 0.8 mg/dL, and 25-hydroxyvitamin D levels of 18 ng/mL (normal >30 ng/mL). A dual-energy x-ray absorptiometry scan of bone mineral density has a T-score of –3.0. What is the best initial therapy for this patient?

A. Calcitonin 200 IU intranasally daily

B. Calcium carbonate 1200 mg and vitamin D 400 IU daily

C. Ethinyl estradiol 5 μg and medroxyprogesterone acetate 625 mg daily

D. Raloxifene 60 mg daily

E. Risedronate 35 mg once weekly, and calcium carbonate 1200 mg and vitamin D 400 IU daily

X-91. A 52-year-old man is found to have an elevated alkaline phosphatase level during routine blood chemistry testing prior to obtaining life insurance after changing jobs. He has a history of hypertension and hyperlipidemia. He previously had a cholecystectomy for gallstone disease. His current medications include losartan 25 mg daily, hydrochlorothiazide 25 mg daily, and rosuvastatin 20 mg daily. He is physically active and has a body mass index of 25.2 kg/m². His only complaint is low back

pain that has been more severe recently. He has had no further evaluation for his back pain. His physical examination is normal. His liver is 10 cm to percussion. It is palpable with deep inspiration at the right costal margin. It is noted to be smooth. Murphy’s sign is negative. There is no warmth or tenderness to palpation over the vertebral bodies of the lumbosacral spine. Laboratory evaluation reveals an alkaline phosphatase level of 468 U/L, alanine aminotransferase level of 22 U/L, aspartate aminotransferase level of 32 U/L, total bilirubin of 1.0 mg/dL, calcium of 9.4 mg/dL, phosphate 3.2 mg/dL, and γ-glutamyl transferase level of 20 U/L. What is the most likely diagnosis?

A. Adverse reaction to rosuvastatin

B. Paget’s disease

C. Primary biliary cirrhosis

D. Retained common bile duct stone

E. Vertebral osteomyelitis

X-92. Which of the following tests is most likely to lead to the diagnosis of the patient in question X-91?

A. Magnetic resonance cholangiopancreatography

B. Magnetic resonance imaging of the lumbosacral spine

C. Plain radiographs of the lumbosacral spine

D. Right upper quadrant ultrasound

E. Serum osteocalcin

X-93. Which of the following biochemical tests is most likely to be within the normal range in a healthy, active individual with Paget’s disease?

A. Serum alkaline phosphatase

B. Serum C-telopeptide

C. Serum calcium

D. Serum N-telopeptide

E. Serum osteocalcin

X-94. A 67-year-old woman presents to the clinic after a fall on the ice a week ago. She visited the local emergency department immediately after the fall, where hip radiographs were performed and were negative for fracture or dislocation. They did reveal fusion of the sacroiliac joints and coarse trabeculations in the ilium, consistent with Paget’s disease. A comprehensive metabolic panel was also sent at that visit and is remarkable for an alkaline phosphatase of 257 U/L, with normal serum calcium and phosphate levels. She was discharged with analgesics and told to follow up with her primary care doctor for further management of her radiographic findings. She is recovering from her fall and denies any long-standing pain or immobility of her hip joints. She states that her father suffered from a bone disease that caused him headaches and hearing loss near the end of his life. She is very concerned about the radiographs and wants to know what they mean. Which of the following is the best treatment strategy at this point?

A. Initiate physical therapy and non–weight bearing exercises to strengthen the hip.

B. Initiate therapy with vitamin D and calcium.

C. Initiate therapy with an oral bisphosphonate.

D. Initiate therapy with prednisone 1 mg/kg, tapering over 6 months.

E. No treatment is required as she is asymptomatic.

X-95. A 32-year-old man is evaluated at a routine clinic visit for coronary risk factors. He is healthy and reports no tobacco use, his systemic blood pressure is normal, and he does not have diabetes. His family history is notable for high cholesterol in his mother and maternal grandparents. Physical examination shows tendon xanthomas. A fasting cholesterol is notable for a low-density lipoprotein cholesterol (LDL-C) of 387 mg/dL. Which of the following is the most likely genetic disorder affecting this individual?

A. Autosomal dominant hypercholesterolemia

B. Familial defective apoB-100

C. Familial hepatic lipase deficiency

D. Familial hypercholesterolemia

E. Lipoprotein lipase deficiency

X-96. All of the following are potential causes of elevated LDL EXCEPT:

A. Anorexia nervosa

B. Cirrhosis

C. Hypothyroidism

D. Nephrotic syndrome

E. Thiazide diuretics

X-97. A 16-year-old male is brought to your clinic by his parents due to concern about his weight. He has not seen a physician for many years. He states that he has gained weight due to inactivity and that he is less active because of exertional chest pain. He takes no medications. He was adopted and his parents do not know the medical history of his biological parents. Physical examination is notable for stage 1 hypertension and body mass index of 30 kg/m². He has xanthomas on his hands, heels, and buttocks. Laboratory testing shows a low-density lipo-protein (LDL) of 210 mg/dL, creatinine of 0.7 mg/dL, total bilirubin of 3.1 mg/dL, haptoglobin below 6 mg/dL, and a glycosylated hemoglobin of 6.7%. You suspect a hereditary lipoproteinemia due to the clinical and laboratory findings. Which test would be diagnostic of the primary lipoprotein disorder in this patient?

A. Congo red staining of xanthoma biopsy

B. CT scan of the liver

C. Family pedigree analysis

D. Gas chromatography

E. LDL receptor function in skin biopsy

X-98. Your 60-year-old patient with a monoclonal gammopathy of unclear significance presents for a follow-up visit and to review recent laboratory data. His creatinine is newly elevated to 2.0 mg/dL, potassium is 3.7 mg/dL, calcium is 12.2 mg/dL, low-density lipoprotein (LDL) is 202 mg/dL, and triglycerides are 209 mg/dL. On further questioning he reports 3 months of swelling around the eyes and “foamy” urine. On examination, he has anasarca. Concerned for multiple myeloma and nephrotic syndrome, you order a urine protein/creatinine ratio, which returns at 14:1. Which treatment option

would be most appropriate to treat his lipid abnormalities?

A. Cholesterol ester transfer protein inhibitor

B. Dietary management

C. HMG-CoA reductase inhibitors

D. Lipid apheresis

E. Niacin and fibrates

X-99. A 40-year-old man is evaluated as part of an executive physical examination. He has read about different screening procedures on the Internet and is interested in being screened for hemochromatosis. He is otherwise healthy and takes only a daily multivitamin. Which of the following tests is the most appropriate first step to screen for this disorder?

A. Genetic testing for C282Y mutation.

B. HFE activity assay.

C. Liver MRI.

D. Screening for hemochromatosis is not cost-effective and not advised.

E. Transferrin saturation, serum iron, and serum ferritin.

X-100. A 55-year-old white male with a history of diabetes presents to your office with complaints of generalized weakness, weight loss, nonspecific diffuse abdominal pain, and erectile dysfunction. The patient has a past history of hypercholesterolemia and takes atorvastatin. The examination is significant for hepatomegaly without tenderness, testicular atrophy, and gynecomastia. Skin examination shows a diffuse slate-gray hue that is slightly more pronounced on the face and neck. Joint examination shows mild swelling of the second and third metacarpophalangeal joints on the right hand. Which of the following studies is most likely to lead to the correct diagnosis?

A. Anti–smooth muscle antibody

B. Ceruloplasmin

C. Hepatic ultrasound with Doppler imaging

D. Hepatitis B surface antibody

E. HFE gene mutation screen

X-101. A 28-year-old man is evaluated for recurrent abdominal pain. He reports that over the last 5 years he has had bouts of severe abdominal pain that is diffuse with distention and not accompanied by vomiting or diarrhea. The pain is not crampy and occurs approximately four to five times per year. One of these episodes was accompanied by hallucinations. He is otherwise healthy, reports engaging in weight lifting, and admits to occasionally using anabolic steroids. During several prior episodes he visited the emergency department and underwent extensive testing including abdominal CT scan with IV and oral contrast. No cause was identified and the symptoms spontaneously resolved after about a day. Which of the following is the next most appropriate step in his evaluation?

A. Endoscopy and colonoscopy

B. Measurement of plasma gastrin level during attack

C. Measurement of urine porphyrobilinogen during attack

D. Prescription of hyoscyamine

E. Referral to psychiatry

X-102. A 58-year-old man is evaluated as part of a life insurance physical examination. He reports feeling well and is without complaints. His past medical history is notable for mild hyperlipidemia and an episode of appendicitis several years ago. He exercises about twice a week playing tennis and does not smoke. His only medication is atorvastatin. On physical examination he is mildly obese, but vital signs and the remainder of the examination are normal. Laboratories are drawn and are normal, with the exception of a uric acid level of 12 mg/dL. Which of the following statements regarding this finding is true?

A. Allopurinol should be prescribed.

B. Careful evaluation for features of insulin resistance should be undertaken.

C. He is at an increased risk of uric acid nephrolithiasis.

D. Most patients with hyperuricemia produce more uric acid than the general population.

E. Over 10 years, most patients with hyperuricemia will develop gout.

X-103. All of the following are associated with hyperuricemia EXCEPT:

A. Cardiovascular disease

B. Gouty arthritis

C. Nephrolithiasis

D. Peripheral neuropathy

E. Urate nephropathy

X-104. A 28-year-old woman seeks counseling before getting pregnant. She had a brother who died at age 9 of Lesch-Nyhan syndrome, and she is a known carrier of the genetic defect. She has no significant past medical history, and her husband has no significant family history. Which of the following statements is true?

A. Her children have no risk of disease since she is not symptomatic.

B. Her husband should be screened for carrying the genetic defect of Lesch-Nyhan syndrome.

C. If she has a daughter, the child has a 50% chance of being a carrier.

D. If she has an affected son, starting him on allopurinol from birth will prevent clinical
manifestations of disease.

E. She should start taking allopurinol to decrease her risk of gout and urate nephropathy.

X-105. A 28-year-old man is admitted to the intensive care unit with fulminant hepatic failure and hemolysis. On further questioning, his family reports that he has been diagnosed with depression for 5 years and been told that his liver is “damaged.” He is taking an antidepressant and occasional ibuprofen, but no other medications. Physical examination is notable for ascites and altered mental status with dystonia. Abdominal CT scan shows no biliary obstruction, but a cirrhotic liver. Which of the following findings would be most likely to confirm the underlying diagnosis?

A. 24-hour urine level of iron

B. Brain MRI showing damage to the basal ganglia

C. Genotype for HFE mutation

D. Schistocytes on peripheral blood smear

E. Slit-lamp ocular examination showing Kayser-Fleischer rings

X-106. Which of the following is the most appropriate initial treatment for the patient in question X-105?

A. Cholestyramine

B. D-penicillamine

C. Liver transplantation

D. Trientine

E. Zinc

X-107. Which of the following is true of Wilson’s disease?

A. Early diagnosis is crucial as highly effective therapy is available.

B. It is inherited in an autosomal dominant pattern.

C. Serum copper levels are usually two to three times above normal.

D. The frequency of disease in the general population is approximately 1%.

E. The liver and pancreas are the most commonly affected organs.

X-108. A 19-year-old girl is evaluated by her primary care physician for recurrent long bone fractures. She has fractured her femur twice and her humerus three times. She has not had an abnormal number of falls and reports also having easy bruising. Aside from these repeated orthopedic injuries, she is otherwise healthy. Physical examination shows mildly disfigured bones; small, amber-yellowish teeth; and bluish-colored sclera. Osteogenesis imperfecta is suspected. Which of the following statements is true regarding this condition?

A. A mutation in type 1 procollagen likely is present in this patient.

B. Bone biopsy is needed for definitive diagnosis.

C. Bisphosphonates have shown long-term success in preventing long bone fractures in this
condition.

D. Fractures in females tend to increase after puberty.

E. Increased bone mineral density may be demonstrated on x-ray absorptiometry.

X-109. More than 90% of patients with Marfan’s syndrome have mutations in which gene?

A. BMPR2

B. COL1A1

C. Fibrillin

D. TGFb

E. Type IV collagen

X-110. A 21-year-old woman comes to the clinic on the advice of her yoga instructor. She recently began classes to increase her activity level and her instructor told her that her joints seemed incredibly flexible, particularly given her inexperience. During the Scorpion exercise, she was able to extend well beyond her classmates. The patient reports good health and a mostly sedentary lifestyle. Throughout her life, she’s been able to perform feats of joint laxity. Her physical examination is notable only for

velvety skin and flexible joints. She is able to hyperextend her wrists at least 90°. Which of the following statements regarding this patient is true?

A. She is at risk of aortic dissection or rupture in the next 20 years.

B. She is at risk of hip dislocation in the next 20 years.

C. She is at risk of uterine rupture during pregnancy.

D. She likely has a mutation in the elastin gene.

E. She likely has a mutation of the fibrillin gene.

ANSWER

X-1. The answer is D. (Chap. 338) Feedback control may be either positive or negative. The primary means of hormone control within the endocrine system is negative feedback. For example, when a steroid hormone level is sensed to be low by the hypothalamus a releasing hormone is released, which effects the release of a stimulatory hormone from the pituitary, and the target gland secretes the steroid hormone and plasma levels rise. The hypothalamus then senses this and decreases the release of the releasing hormone. This is employed by the endocrine system to control levels of thyroid hormone, cortisol, gonadal steroids, and growth hormone. The renin-angiotensin-aldosterone axis is independent of the pituitary and hypothalamus and involves the liver, lungs, and kidney.

X-2. The answer is E. (Chap. 338) Hormone resistance may be due to receptor mutations or signaling pathway mutations, or, most commonly, postreceptor alterations. Type 2 diabetes mellitus and leptin resistance are examples of postreceptor alterations resulting in hormone resistance. Pheochromocytoma and Graves’ disease are examples of organ hyperfunction, Hashimoto’s thyroiditis and Sheehan’s syndrome are diseases of organ hypofunction. In the case of Sheehan’s syndrome, the affected organ is the pituitary gland.

X-3. The answer is C. (Chap. 338) Intermittent pulses of GnRH are necessary to maintain pituitary sensitivity to the hormone. Continuous exposure to GnRH causes pituitary gonadotrope desensitization, which ultimately leads to decreased levels of testosterone. The relationship between GnRH and LH/FSH is a positive feedback loop where GnRH causes secretion of LH and FSH. Receptor translocation from the cytoplasm into the nucleus occurs with certain hormones (e.g., glucocorticoid); however, this receptor phenomenon is not specific to any regulatory mechanism. GnRH does not promote the production of sex hormone–binding globulin. Moreover, although binding globulins can decrease the amount of bound hormone measured in the serum, abnormal levels of binding globulins usually do not have any clinical significance because the free hormone levels usually increase.

X-4. The answer is B. (Chap. 338) With few exceptions, hormone binding is highly specific for a single type of nuclear receptor. The mineralocorticoid-glucocorticoid hormones are a notable exception because the mineralocorticoid receptor also has a high, but not greater, affinity for glucocorticoid. An enzyme (11 β-hydroxysteroid dehydrogenase) located in renal tubules inactivates glucocorticoid, allowing selective responses to mineralocorticoid. When there is glucocorticoid excess, the enzyme becomes oversaturated and glucocorticoid can exhibit mineralocorticoid effects. This effect is in contrast to the estrogen receptor, where different compounds confer unique transcription machinery. Mineralocorticoid hormones do not have serum-binding proteins. Examples of hormones that circulate with serum-binding proteins are T₄, T₃, cortisol, estrogen, and growth hormone. Most binding protein

abnormalities have little clinical consequence because the free concentrations of the hormone often remain normal.

X-5. The answer is C. (Chap. 339) Hormones produced by the anterior pituitary include

adrenocorticotropic hormone, thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, prolactin, and growth hormone. The posterior pituitary produces vasopressin and oxytocin. The anterior and posterior pituitary has a separate vascular supply, and the posterior pituitary is

directly innervated by the hypothalamic neurons via the pituitary stalk, thus making it susceptible to shear stress–associated dysfunction. Hypothalamic control of anterior pituitary function is through secreted hormones; thus it is less susceptible to traumatic injury.

X-6. The answer is B. (Chap. 339) The patient has evidence of Sheehan’s syndrome postpartum. In this syndrome, the hyperplastic pituitary postpartum is at increased risk for hemorrhage and/or infarction. This leads to bilateral visual changes, headache, and meningeal signs. Ophthalmoplegia may be observed. In severe cases, cardiovascular collapse and altered levels of consciousness may be observed. Laboratory evaluation commonly shows hypoglycemia. Pituitary CT or MRI may show signs of sellar hemorrhage if present. Involvement of all pituitary hormones may be seen, though the most acute finding is often hypoglycemia and hypotension from the failure of adrenocorticotropic hormone. The hypoglycemia and hypotension present in this case suggest failure of the glucocorticoid system; thus treatment with a corticosteroid is indicated. There is no evidence of sepsis; thus antibiotics and drotrecogin alfa are not indicated. With a normal hematocrit and no reported evidence of massive hemorrhage, packed red cell transfusion is unlikely to be helpful. Although thyroid-stimulating hormone production is undoubtedly low in this patient, the most immediate concern is replacement of glucocorticoid.

X-7. The answer is D. (Chap. 339) Functional pituitary adenoma presentations include acromegaly, as in this patient, prolactinomas, and Cushing’s syndrome. Hypersecretion of growth hormone underlies this syndrome in patients with pituitary masses, though ectopic production of growth hormone, particularly by tumors, has been reported. Because growth hormone is secreted in a highly pulsatile fashion, obtaining random serum levels is not reliable. Thus, the downstream mediator of systemic effects of growth hormone, IGF-1, is measured to screen for growth hormone excess. IGF-1 is made by the liver in response to growth hormone stimulation. An oral glucose tolerance test with growth hormone obtained at 0, 30, and 60 minutes may also be used to screen for acromegaly, as normal persons should suppress growth hormone to this challenge. Serum prolactin level is useful to screen for prolactinomas; 24-hour urinary free cortisol and ACTH assay are useful screens for Cushing’s disease.

X-8. The answer is B. (Chap. 339) Hyperprolactinemia is the most common pituitary hormone

hypersecretion syndrome in both men and women. Although pituitary adenoma is a frequent cause, there are several physiologic, medication-related, and potentially reversible etiologies. Prolactin is normally elevated during pregnancy and lactation, though levels should fall to normal within 6 months of cessation of breastfeeding. Nipple stimulation, sleep, and stress may all increase prolactin levels. Systemic disorders such as chronic renal failure and cirrhosis may also cause elevated prolactin levels. Prolactin levels are also typically elevated after generalized seizures, which may be useful in the evaluation of pseudoseizures. Drug-induced hypersecretion is associated with dopamine receptor blockers, dopamine synthesis inhibitors, opiates, H₂ antagonists, imipramines, selective serotonin

reuptake inhibitors, and calcium channel blockers. Hypothalamic-pituitary stalk damage may also cause hyperprolactinemia. Rathke’s cysts, which are benign intrasellar lesions, may produce endocrinologic abnormalities similar to pituitary adenomas.

X-9. The answer is E. (Chap. 339) Tumors arising from the lactotrope cells of the pituitary account for half of all functioning pituitary tumors and most commonly affect women. The most common presentations are amenorrhea, infertility, and/or galactorrhea. Micro-adenomas rarely progress to

become macroadenomas. For symptomatic disease, the primary goals of therapy are control of hyperprolactinemia, reduction of tumor size, restoration of menses and fertility, and resolution of galactorrhea. Usually oral dopamine agonists, such as carbergoline and bromocriptine, are used for this purpose.

X-10. The answer is C. (Chap. 339) Adult growth hormone deficiency is usually caused by hypothalamic or pituitary damage. Because growth hormone is no longer important for achieving stature, the presentation is different from childhood growth hormone deficiency. Although growth hormone has direct tissue effects, it primarily acts through increasing secretion of IGF-1, which in turn stimulates lipolysis, increases circulating fatty acids, reduces omental fat mass, and enhances lean body mass. Thus, deficiency of growth hormone causes the opposite effects. In addition, hypertension, left ventricular dysfunction, and increased plasma fibrinogen levels may also be present with deficient growth hormone. Reduced, not increased, bone mineral density may also occur in adults with growth hormone deficiency.

X-11. The answer is E. (Chap. 339) The patient has a clinical presentation consistent with Cushing’s syndrome. Although many cases of inappropriate elevation of ACTH are due to pituitary tumors, a substantial proportion are due to ectopic ACTH secretion. Clues to this diagnosis include a rapid onset of hypercortisolism features associated with skin hyperpigmentation and severe myopathy. Additionally, hypertension, hypokalemic metabolic alkalosis, glucose intolerance, and edema are more prominent in ectopic ACTH secretion than in pituitary tumors. Serum potassium below 3.3 mmol/L is present in 70% of ectopic ACTH cases, but in less than 10% of pituitary-dependent Cushing’s syndrome. ACTH levels will be high, as this is the underlying cause of both types of Cushing’s syndrome. Corticotropin-releasing hormone is rarely the cause of Cushing’s syndrome. Unfortunately, MRI of the pituitary gland will not visualize lesions less than 2 mm; thus occasional sampling of the inferior petrosal veins is required, but this is not indicated in the case presented at this time in the evaluation.

X-12. The answer is C. (Chap. 339) The patient has panhypopituitarism and is unable to make TSH; thus her plasma TSH level will always be low, regardless of the adequacy of her T₄ replacement. A

free T₄ level will allow the determination of whether her plasma level is in the normal range of thyroid

hormone. This, coupled with her symptoms, will aid in the determination of proper levothyroxine dosing. There is no evidence of recurrent disease clinically; thus MRI is not useful. She is unlikely to have primary thyroid disease, and T₄ level is unknown presently, so thyroid uptake scan is not indicated

at this time.

X-13. The answer is A. (Chap. 339) The diagnosis of Cushing’s syndrome relies on documentation of endogenous hypercortisolism. Of the list of choices, the most cost-effective and precise test is the 24­hour urine free cortisol. Failure to suppress plasma morning cortisol after overnight suppression with 1 mg dexamethasone is an alternative. Most ACTH-secreting pituitary adenomas are less than 5 mm in diameter, and approximately half are not detected even with sensitive MRI. Further, because incidental microadenomas are common in the pituitary, the presence of a small pituitary abnormality on MRI may not establish the source of ACTH production. Basal plasma ACTH levels are used to distinguish between ACTH-independent (adrenal or exogenous glucocorticoid) and ACTH-dependent (pituitary, ectopic ACTH) sources of hypercortisolism. Mean basal ACTH levels are higher in patients with

ectopic ACTH production than in patients with pituitary ACTH adenomas. There is significant overlap in ACTH levels, however, and this test should not be used as an initial diagnostic test. Rarely, patients have Cushing’s syndrome and elevated ACTH due to a CRH-releasing tumor. In this case, CRH levels are elevated. Inferior petrosal venous sampling can be used to identify a pituitary source of ACTH secretion when imaging modalities do not reveal a source.

X-14. The answer is B. (Chap. 339) The identification of an empty sella is often the result of an incidental MRI finding. Typically these patients will have normal pituitary function and should be reassured. It is likely that the surrounding rim of pituitary tissue is functioning normally. An empty sella may signal the insidious onset of hypopituitarism, and laboratory results should be followed closely. Unless her clinical situation changes, repeat MRI is not indicated. Endocrine malignancy is unlikely, and surgery is not part of the management of an empty sella.

X-15. The answer is A. (Chap. 340) The patient has a classic presentation for a patient with idiopathic diabetes insipidus with long-standing urinary frequency, thirst, enuresis, and nocturia. Patients may also report mild fatigue from frequent nocturnal awakenings. Diabetes insipidus may be nephrogenic or central, though this case presentation is not specific for either etiology. Diabetes insipidus is confirmed by measurement of 24-hour urine volume, which is more than 50 mg/kg per day (3500 mL in a 70-kg male), and urine osmolarity of greater than 300 mosmol/L. In order to differentiate central from nephrogenic diabetes insipidus, history may be useful in determining prior head trauma, neuro-surgery, or granulomatous disease that may damage the neurohypophysis, or may suggest a medication such as lithium known to cause nephrogenic diabetes insipidus. The fluid deprivation test, in which a patient is deprived of fluid and hourly urine output; body weight; plasma osmolarity and/or sodium concentration; and urine osmolarity are measured. If fluid deprivation confirms persistent elevation of urine osmolarity, then severe diabetes insipidus is again confirmed. Desmopressin can be administered at this point and if the electrolyte, urinary, and clinical variables are corrected, central disease is confirmed. In nephrogenic diabetes insipidus, there is minimal response to ADH, as the primary defect is in the kidney. MRI of the brain is not useful until after central disease is confirmed.

Date: 2016-04-22; view: 583