High Yield USMLE Cases - A Must For A Great USMLE Score
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Q)Very important in clinics/tests...you have a patient with angina. You need to DECREASE heart rate and cardiac contractility and block coronary vasospasm. Which drug, Verapamil or Nifedipine will do the work?
A) Verapamil will do it. Nifedipine, another Ca channel blocker, does not do this well.
Q) Very important in clinics/tests: What is the rate limiting committed step in de novo purine synthesis? Is it:
1) Ribose 5 phosphate > PRPP or
2) PRPP > 5 phosphoribosylamine?
A) PRPP > 5 phosphoribosylamine, CONFUSING...but this is because Ribose 5 phosphate > PRPP is the FIRST step, but not the rate limiting one because PRPP is also utilized in PYRIMIDINE synthesis and in base salvage.
Case on RBCs: If I present you with a mature RBC named George Bush, tell me, True or False:
Q) In the RBC, lactate is converted to pyruvate for use in gluconeogenesis.
A) False, recall that gluconeogenesis occurs only in the liver and kidneys.
Q) In RBCs there is a glycolysis where there are 2 ATP made. The two reduced NADH are then used to convert pyruvate into lactate. Is this true or false?
A) TRUE, some think it is acetyl CoA, but they are wrong.
Q) A mature RBC uses the pentose phosphate pathway for the formation of NADPH. Why is this needed?
A) To maintain glutathione in a reduced state.
Q) What is the reduced glutathione used for in the RBC?
A) You need it to maintain the integrity of the cell membrane!
Q) What is the most common benign soft tissue tumor in adults.
A) LEIOMYOMA, do you know what a gross specimen looks like?
Q) The most common soft tissue SARCOMA. What do you say?
A) Malignant fibrous histiocytoma.
Q) As we just discussed, malignant fibrious histiocytoma is found where and in whom usually.
A) often in men, older, and involves the limb bones and retroperitoneum.
Q) True or False: Lipomas often will progress to liposarcomas, given enough years.
Also, where are they most often found?
They are most often benign and found around the neck and torso!
Q) We discussed LIPOMAS (also known as uterine fibroids), are very common, but different from Leiomyomas. But what about leiomyoSARCOMAS? What are they?
A) They are malignant tumors of SMOOTH muscle origin. So, you will see lesions in the uterus, GI walls, and blood vessels.
Q) What exactly is a rhabdomyoma? Benign or Malignant?
A) Benign, they are benign tumors of skeletal or cardiac muscle. IT is the Second most frequent tumor of the heart. Myxomas are the most common here.
Q) What nucleotide cannot be a substrate of primase? (choices: ATP, TTP, UTP, GTP).
A) Think and recall that TTP has thymidine. Because primase makes RNA primers in DNA replication, only RIBOnucleotides can be used.
Q) You live in a house called "Sand and Fog". Again, your friend, Jennifer Connolly comes in and steps on a nail. You quickly give her tetanus immune globulin. Does this neutralize circulating toxin, toxoid, or fixed toxin on nerve tissue?
A) Cirulating toxin.
Q) Case: Your attending pulmonologist walks in and asks YOU if a flowmeter tracing depicts the relationship between flow rate during a Forced Vital Capacity (FVC) and LV (Lung Volume). An FVC starts at the point of total lung capacity (TLC) and ends at Residual Volume (RV). Is all this true or false?
A) True, KNOW also that a restrictive lung disease will DECREASE BOTH TLC and RV.
Q) T or F: You have a patient named Don Johnson who has partial seizures. He is refractory to phenytoin and carbamazepine. Your med student suggests ethosuximide. Is she correct?
A) NO! Ethosuximide works only for generalized absence seizures.
Q) Case: A previously healthy 7 year old girl suffers from a 2 week history of fever, fatigue, weight loss, muscle pain, and headache. He also has a heart murmur, petechiae, and splenomegaly. What disease does she have?
A) Endocarditis, with vegetations from Streptococcus or Staphylococcus infection.
Q) case: You are seeing a 19 year old primiparous woman with toxemia in her last trimester of pregnancy treated with MgSO4. She delivers full term a 2 kg infant with poor APGAR score. Labs have a persistent hematocrit of 80%, platelets of 110,000, glucose 40 mg/dL, Mg 2.5 mEq/L, and Calcium 10 mg/dL. Later this infant has a seizure. What is the cause?
A) Pt has polycythemia induced seizures. The Mg IMPLIES that she had PREGNANCY INDUCED HYPERTENSION. This results in nutritional deprivation and hypoxemia, and erythrocytosis. KNOW that a persistent hematocrit over 65% in a neonate baby results in HYPERVISCOSITY and seizures.
Q) Which bug more often causes congenital infections, Toxoplasma gondii, Mycobacterium tuberculosis, Trichomonas?
A) REMEMBER the TORCH! T=Toxoplasma...the others seldom are implicated.
Q) Case: A Turner's syndrome patient at infancy. (45, X,O). What lesion is predominant in the neck, heart and kidneys?
A) In the neck, you will see redundant skin folds. In the heart, you often will see coarctation of the aorta, HTN, bicuspid aortic valve, and sometimes horseshoe kidney.
Q) Failure to give vit K to a newborn patient will result in elevated prothrombin or thrombin time? Plus, what clotting factors are affected?
A) PROthrombin time, Factors II, VII, IX and X are affected.
Q) Your pregnant patient is 35 weeks. Which of the following should you NOT give to her (Pick from penicillin, phenytoin, heparin, and propranolol)?
A) Of these, propranolol is contraindicated at this 3rd trimester. Bradycardia and apnea can result. HOWEVER, phenytoin recall is contraindicated usually in the FIRST trimester. The other two are safe.
Q) Woman with no prenatal care delivers small for date baby. She told you she had multiple sexual partners during her pregnancy and before. The PE of the baby has hepatosplenomegaly, noted lymphadenopathy, and nasal discharge like the snuffles. What test do you think of getting to confirm the dx?
A) FTA-ABS for syphillis. Choose PENICILLIN for Rx.
Q) A 7 month old pt. comes in with a resting HR of 50. PE reveals NO rash, and NO cardiomegaly. But electrocardiogram reveals d-looped ventricles. FH is significant for SLE. What is causing the bradycardia?
A) Most likely, a congential complete heart block. Lyme disease can be ruled out because there is no tick bite, and cardiomyopathy can be ruled out because there is NO cardiomegaly on x-ray.
Q) What and where is the anterior recess of the ischiorectal fossa?
A) A fat filled space below the pelvic diaphragm, it is in between the inferior space of the of pelvic diaphragm and the superior fascia of the urogenital diaphragm.
Q) A 37 y.o. male patient of yours has GI symptoms and feels high strung a LOT for no apparent reason, sweating AND dry mouth. Does he have panic disorder or Generalized anxiety disorder?
A) Generalized anxiety disorder...rule out panic disorder because panic disorder is usually triggered by a known cause. Give anxiolytics for meds.
Q) Someone, a 27 year old male goes to the Southern-Eastern states for a camping trip. He gets Rocky Mountain Spotted Fever. Except for the rashes and fever, what is a typical medication you would use to treat? What is the MOA of the bug? What test is helpful?
A) Use either doxycycline or tetracycline combined with chloramphenicol. The MOA of the bug is a vasculitis resulting from endothelial invasion by Rickettsial buggies. The test of choice now is the indirect florescent antibody (IFA) test. OR you can use a Giemsa stain under light microscopy.
Q) Case: You see a 5 year old pt. with a history of a URI like symptoms that preceded a rash that started from his face and spread downward (there were no Koplick spots). Lymphadenopathy may OFTEN be present, particularly in the posterior auricular, posterior cervical, and suboccipital chains. What is the dx? What is the treatment?
A) This is Rubella. Treatment is supportive with Tylenol and Benadryl for the headaches and itching.
Q) A child patient of yours comes in. Your attending tells you this is NOT RUBELLA. He had a high fever for 3 days and the rash that followed started on the trunk and then spread from there but missed his face. The condition is an acute benign disease of childhood characterized by a history of a prodromal febrile illness lasting approximately 3 days, followed by defervescence and the appearance of a faint pink maculopapular rash. Bug please?
Q) Case: Pt of yours comes in with crops of papular, vesicular, pustular lesions starting on the trunk and spreading to the extremities. Lesions are asynchronous (happening at different times). What is this?
Q) This time, you see a young patient with ulcers on his tongue and oral mucosa. You also see a maculopapular vesicular rash on the hands and the feet surfaces (key finding). What disease is this?
A) Hand foot and mouth disease
Q) A 25 year old male patient of yours comes in with spironolactone overdose and HYPERKALEMIA. He gets muscle weakness and tetany. His potassium level is 7.4...no hemolysis. Which EKG change is NOT consistent with hyperkalemia? (pick between notched PR segment, ST depression, wide QRS complex, P wave loss, T wave elevation).
A) You WON'T see notched PR segments, but you WILL see all the others.
Q) Case: You see the same patient with Hyperkalemia. What are a few OTHER causes of this?
A) You'll see this in acute or chronic renal failure, especially in patients who are on dialysis.
Other causes include:
Trauma, including crush injuries (rhabdomyolysis), or burns.
Ingestion of foods high in potassium (eg, bananas, oranges, high-protein diets, tomatoes, salt substitutes).
Meds - Potassium supplements, potassium-sparing diuretics, nonsteroidal anti-inflammatory drugs (NSAIDs), beta-blockers, digoxin, and digitalis glycoside.
Q) Case: Still looking at Hyperkalemia. We are dealing with a HYPERacute case of it. What med is better, Calcium gluconate or Kayexalate?
A) Calcium gluconate is better, its onset of action is as quick as 5 minutes while kayexalate may take 2-10 hours to take effect. HOwever, know that Calcium gluconate does not really affect TOTAL body K+ stores, but rather is CARDIOprotective
Q) Pt: A 6 year old child named Kill Bill presents with tachycardia at 230 beats per minute, no fever. The ECG shows a narrow complex tachycardia seen (no signs of atrial flutter). One dose of ADENOSINE makes the sinus rhythm normal with pre-excitation noted. There is NO cardiomegaly seen on radiograph. What is this? Could it be sinus tachycardia?
A) HARD HARD question. The pre excitation seen after conversion with adenosine is Wolff-Parkinson White syndrome. Sinus tachy is not likely because the patient is afebrile with no cardiomegaly.
Q) Case: Because this is so common, what is the difference in presentation between strabismus and amblyopia?
A) Strabismus is an eye that cannot align properly and amblyopia is the impairment of vision without detectable organic lesion of the eye.
Q) Case: A middle aged patient of yours tried to kill herself by injesting a bottle of antipsychotics with anticholinergic activity....can she acutely die from cardiac arrhymias?
Q) Case: True or False: Besides mental slowness, iron toxicity can cause seizures.
Q) Case: Which one, (CCK, secretin, or bile acid levels in the plasma), determine the rate of bile secretion by hepatocytes?
A) Plasma levels of bile acids...tricky tricky. Stuff like secretin and parasympathetic innervation works at the LEVEL of the biliary ducts...NOT the hepatocytes.
Q) case: You encounter a 34 y.o. patient screaming in pain because he has a kidney stone. You find that the stone is a struvite or staghorn stone. What bug does he likely have? Is the stone calcium? What minerals are part of the stone? Is the urine acidic or alkaline?
A) He likely has a Proteus infection producing urease. The stone is NOT the most common Calcium stones. The minerals are M.A.P. or Magnesium, Ammonia, and Phosphate. The urine is ALKALINE (think ammonia).
Q) Case: Oh darn! Your patient has cystathionine synthetase deficiency. What disease is this associated with? What Amino Acid is elevated? How do the patients present clinically? What do they need to remove from their diet?
A) Homocystinuria is the dx. The amino acid elevated is methionine since its conversion is impossible. The patients present as a Marfan's body w/ scoliosis, dislocated eye lenses, mild mental retardation, thrombosis. The restriction of proteins like sulfhydryl groups leads to very low protein, foul tasting diets.
Q) A patient of yours has galactose 1 phosphate uridyl transferase deficiency. What enzyme is missing? What is the clinical presentation? What is the treatment?
A) This dx is the most common error of carbohydrate metabolism, galactosemia. Glycolysis is affected, and you see evidence of liver failure, direct hyperbilirubinemia, coag disorders, renal problems (acidosis, glycosuria), emesis, and sepsis. TREAT by eliminating all formulas and foods with galactose.
Q) What is the enzyme disease associated with ornithine transcarbamylase deficiency? How is it inherited? What toxic metabolite forms? MOA? Clinical presentation? Treatment?
A) This...OTCD...is a urea cycle defect inherited in an X-linked fashion. Ornithine couples with carbamylphosphate to make citrulline. If the enzyme is def., ornithine builds up and then urea cannot be made and excreted. AMMONIA builds up instead, and within only 24 hours, the newborn baby will become lethargic and have seizures. DIAGNOSIS by measuring the orotic acid levels in the urine. TREAT with a low fat diet and alternate pathways to excrete nitrogen via benzoic acid and phenylacetate.
Q) Case: Your patient has a respiratory disorder and is cyanotic. He comes in with a normal arterial oxygen tension (PaO2) and a LOW arterial oxygen saturation (SaO2). Your med student rushes to give oxygen therapy and the patient is STILL cyanotic. What does he have? (Pick either Right to left SHUNT, Methemoglobinemia, Respiratory Acidosis). Why?????????? How do you treat?
A) He has Methemoglobinemia. IRON needs to be in the ferrous form (+2) to be able to bind oxygen. In this dx, the IRON is in the ferric form (+3). So giving O2 does not help. You must give methylene blue which aids in the conversion.
Q) CASE: Please refer to the previous HY Concept 995...why is the answer not right to left shunt? (This is a crucial point)
A) Because, while O2 therapy has very little effect, BOTH oxygen tension (PaO2) AND oxygen saturation (SaO2) are LOW. Recall that in methemoglobinemia, the oxygen gas exhange is NOT affected in the lungs, so PaO2 is NORMAL there!
Q) Speaking of RBCs, a 14 month old male child presents with a hemoglobin of 7.6 and a hematocrit of 24%. The MCV is 65 and the adjusted reticulocyte count is 1.0. Is this ineffective erythropoiesis or not?
A) An ARC less than 2.0 is ineffective erythropoiesis for the anemia, an anemia with ARC more than 2.0 signals hemolysis or blood loss and decent erythropoiesis.
Q) Case: Everyone is going to have to do this procedure: Checking for the red reflex...what happens though if you see a reflection from a white mass within the eye giving the appearance of a white pupil? What diseases can cause this?
A) Congenital cataracts, Retinoblastoma, Glaucoma...RECALL if you see signs of a retinal hemorrhage, think SHAKEN BABY SYNDROME and protect the baby!
Q) Case: One of your patients comes in with blood streaked feces. He is an 19 month old. Fecal Occult blood test is positive. What diagnoses is MOST common here?
A) Anal fissure.
Q) The 19 month kid with the bloody stool.
"Why can't this be IBD?"
"Why can't this be Necrotizing enterocolitis?"
"Why can't this be a Mallory-Weiss tear?"
"What can't this be peptic ulcer disease?"
(So what do you say to each?)
A) Tell him that IBD (Chron's and Ulcerative Colitis) and necrotizing enterocolitis appears later in childhood, and a Mallory Weiss tear and PUD will produce dark MELENA instead!