What goes through my head when I get a calcium question...

#1: Is calcium too high or too low?
#2: What is the phospate level?

The question stem might not give calcium levels so I might have to look for the S/S of hyper or hypocalcemia. Hypercalcemia is classically summarized by the mnemonic "stones, bones, abdominal groans and psychic moans". Hypocalcemia is best remembered by the 2 signs associated with it, Chovstek's sign and Trousseau's sign. The tricky part is that hypocalcemia causes tetany, not hypercalcemia. Most people get this backwards.

The phosphate level tells me who is causing the problem, vitamin D or PTH. The "job" of PTH is to increase free calcium and to decrease phosphate. This leads to a high calcium and a low phosphate. The "job" of vitamin D is to increase both calcium and phosphate, increasing bone mineralization.

So if calcium is high and phosphate is low, PTH did its job. If calcium is low and phosphate is high, PTH is sleeping and should be fired.

If both calcium and phosphate are high, vitamin D did its job. If both are low, vitamin D is slacking.

Next post: what to do with your newfound information on PTH and vitamin D activity.

Answer to the Endocrine Question

This question really boils down to a calcium question and the choices should be broken down into what causes hypocalcemia and what causes hypercalcemia.

WRONG ANSWERS:
Choice (A) lung cancer was put there because of the distractor in the stem, the possibility of squamous cell lung cancer and the paraneoplastic syndrome associated with hypercalcemia and PTHrp (PTHrp is not measured when you get a PTH level. PTH should be suppressed due to the high calcium levels).

Choice (B) primary hyperparathyroidism is another distractor because the patient has a high PTH level. But when does primary hyperparathyroidism ever cause hypocalcemia? Never!

Choice (D) thyroidectomy done by a sloppy surgeon can sometimes cause hypocalcemia due to the inadvertant removal of the parathyroid glands. This would indeed cause hypocalcemia, but, PTH would NEVER be elevated.

Choice (E) plasma cell infiltration of the bone marrow referred to multiple myeloma, which is in the differential diagnosis of HYPERcalcemia. PTH would be suppressed.


ANSWER:
Choice (C) renal failure is the answer because it is the only choice that can cause hyperphosphatemia, hypocalcemia and elevated PTH. The history of diabetes is subltly included but it is not necessary to answer this question. I used to get confused with renal disease until I boiled it down to, "don't give chronic renal failure patients Coca Cola." The main problem with calcium in renal failure is due to the high phosphate levels that the kidneys can't get rid of. The phosphate and the calcium combine in the blood. This lowers the calcium. The parathyroids go into panic mode and try to raise calcium by destroying the bones (osteitis fibrosa cystica).

What's in a name... Baclofen

If you want a clue on the MOA of baclofen, add "GA" to the front of the name to make GAbaclofen. Baclofen is a GABA B agonist used for its muscle relaxing properties.

Find the Gold Standard... Endocrine question

A 65 y/o male is admitted to the hospital for a lower lobe pneumonia. His past medical history includes diabetes mellitus, COPD, and hypertension. He is a chronic smoker, with a 50 pack year smoking history. Upon admission to the hosptital, his lab report shows decreased serum calcium levels, elevated phosphate levels, and and elevated intact serum PTH levels. What is the most likely cause of abnormal lab values?

A. Lung cancer
B. Primary hyperparathyroidism
C. Renal failure
D. Thyroidectomy
E. Plasma cell infiltration in the bone marrow

Please leave you answer in the comments section along with what you think is the "gold standard" of this question. I will post my reponse tomorrow.

Find the Gold Standard!

A 35-year-old diabetic woman presents to her gynecologist with complaints of burning on urination for the past 2 days. Dipstick test of her urine demonstrates markedly positivity for leukocyte esterase, but no reactivity for nitrite. Urine culture later grows out large numbers of organisms. Which of the following bacteria are most likely to be responsible for this patient's infection?

A. Enterobacter sp.
B. Enterococcus faecalis
C. Escherichia coli
D. Klebsiella pneumoniae
E. Pesudomonas aeruginosa



The gold standard in this question is not the culture, because all five of these bugs will grow on agar. Here the gold standard is the "no reactivity for nitrite." Production of nitrites is typically found in gram negatives when the converted nitrate to nitrite (via reductase). So this question boils down to which one of the bugs is the gram positive? Enterococcus (B) is the answer to the question, but I wanted to bring the trickiness of the name Enterococcus to everyones attention. It sounds too similar to the gram negatives sp. Enterobacter. I have confused these two since I opened my first micro book. Nowadays, I consciously slow down my reading whenever I see the word "entero." Enterotoxin and endotoxin are often confused as well. So be careful!

2 for 1 Deal... Hemolytic Diseases with Gallstones.

There are two hemolytic diseases with bilirubin stones as complications. One is sickle cell anemia, and the other is hereditary spherocytosis. One quick and dirty way to tell them apart is by looking at the spleen size. Sickle cell patients will have a spleen the size of a walnut buy the age of 2. Hereditary spherocytosis is the only hemolytic anemia with an enlarged spleen.

What's in a Name: HUS and TTP

Hemolytic uremic syndrome often follows an infection from E. coli O157:H7. HUS should really be called H.U.T.S (hemolysis, uremia, thrombocytopenia syndrome). Questions with syndromes are tricky becuase most people miss them because instead of saying directly hemolysis, uremia, and thrombocytopenia, the stem will usually say that the patient has increased LDH and decreased haptoglobin, elevated BUN and creatinine, and petechiae.

If you add altered mental status and fever to HUTS, you get TTP.

The way that I see the "big picture" and avoid getting lost in the details of a question, I read through the stem pretty quickly, painting a picture of whats going on in the patient. If the AST/ALT is elevated, the liver is likely involved. If there is hemoptysis, the lungs are invovled.

I then do some very basic math in my head... Liver + Lung = could be alpha 1 antitrypsin deficiency in a young, non-drinker with cirrhosis and hemoptysis.

Question Dissection

Question:

A mailman gets a severe bite wound from a pit bull guarding a junkyard. The wound is cleansed and he receives a booster injection of tetanus toxoid and an injection of penicillin G. Several days later, the wound is inflamed and purulent. The exudate is cultured on blood agar and yields gram-negative rods. Antibiotic sensitivity tests are pending. The most likely agent to be isolated is

A. Actinomyces israelii

B. Leptospira interrogans

C. Clostridium tetani

D. Pasteurella multocida

E. Capnocytophagia canimorsus





Answer: (D) Pasteurella multicida

It is important to know the infections you get from a cat/dog bite, scratch, and urine.

Bite: Pasteurella multicida
Scratch: Bartonella henselae
Urine: Leptospira interrogans

Of the above choices, only two are gram negative rods, Pasteurella and Capnocytophagia. Actinomyces is "actin like a myces" so it is a gram positive filamentous rod. Leptospira is a spirochete. Clostridium is a gram positive rod. The tricky one is (E) Capnocytophagia canimorsus. If you look at the name, Capnocytophagia, you can see the "capno" and the "cytophagia." "Capno" refers to carbon dioxide and "cytophaga" means "cell eater." Capnocytophagia is a fastidious grower which requires a microaerophilic environment to grow so it probably wouldn't grow on the above blood agar.

One of the most my important resources is my Stedman's medical dictionary. I have it on my Blackberry, computer, and Palm. Stedman's is nice because it gives you the Latin and Greek roots of the words. How can you answer a question if you don't know the difference between sclerosis and stenosis? In the question above, knowing that "capno" meant carbon dioxide, gave me enough information to get a similar question right on my USMLE Step 1.

What's in a Mnemonic: encapsulated organisms

One of the most high yield mnemonics in microbiology is the one for encapulated organisms:

"Some Nasty Killers Have Some Capsule Protection":

Streptococcus pneumoniae
Neisseria meningitidis
Klebsiella pnemoniae
Haemophilus influenzae
Salmonella typhi
Cryptococcus neoformans
Pseudomanas aeruginosa

Most people know this mnemonic. However, many people don't realize how many questions they can answer just by memorizing just one sentence.

The following are uses for the above mnemonic:

1. If the question presents a patient missing anything needed to kill encapsulated organisms (eg spleen, IgG, C3b, macrophages, etc.), they are at increased risk for infections from the above bugs.
2. Diseases that are infamously susceptible to encapsulated organisms:
   
1. anyone who doesn't have a functional spleen (eg: sickle cell)
2. Bruton's agammaglobulinemia
3. If an organism has a capsule, some vaccines are made against the capsule
   
1. Pneumococci
2. Meningococci
3. H. influenzae type b
4. Usually, the capsule is a major virulence factor for the above organisms.
5. If the question mentions a positive Quellung reaction, look for one of the above bugs for an answer.
6. Big mucoid colonies on blood agar is Klebsiella (from a big mucoid capsule)
   

How to find the gold standard in each USMLE question.

A 68 year old male presents with 5 days of fever, non-productive cough, confusion, and a chest x-ray showing non-specific pneumonia. He works in a community hospital with a desk underneath an air-conditioning vent. A sputum culture is taken and it grows a large number of organisms on blood agar. What is the most likely cause of his pneumonia?

The answer to this question could be a number of things, but the one thing I'm certain about, is that the answer is NOT Legionella pneumophilia. True, he has exposure to air-conditioning and presents with the typical symptoms of Legionella pneumonia, but when did Legionella ever grow on normal blood agar? It is a fastidious organism that grows on charcoal yeast extract (CYE) agar. Most of the people I ask know the culture requirements of Legionella, but those same people still answer Legionella for the preceding stem. Why does this happen? And how do you prevent yourself from making the same mistake again?

The way I avoid making this mistake on a multiple choice test is by finding the "gold standard" information in each question. Usually the gold standard information is found in the pathology or microbiology report, followed by blood tests, radiology reports, physical exam, patient history, and finally by risk factors, in that order. A good example of this is found in the treatment of cancer. Would you be willing to give a patient months of chemotherapy based on a just a history of smoking and a cough? How about a single calcified nodule in the lungs? How about a pathology report showing small cell lung carcinoma? I think most of us would rely on the later for our treatment decisions.

The same logic can be applied to answering our original scenario. Would you give this patient the drug of choice for Legionella, a macrolide, based on the history of exposure to air conditioners? If that is how medicine was practiced, I would be on erythromycin right now. The differential diagnosis of diseases in people who were exposed to air conditioners includes just about ALL diseases.

Here is my "gold standard" list from most reliable to least reliable.

1. Pathology/histology reports
2. Microbiology cultures/stains
3. Blood tests including CBC, electrolytes, tumor markers, hormone levels
4. Radiology reports
5. Vitals and physical exam
6. Symptoms
7. Patient's past medical history
8. Patient's age
   
9. Patients risk factors
   
10. Family history

Is it jaundice... or too many carrots?

• TOO MUCH BILIRUBIN BEING PRODUCED ("hemolytic jaundice")
• Ineffective hematopoiesis", i.e., normoblasts dying in the bone marrow
• Thalassemias (even mild ones like beta-thal minor)
• Megaloblastic anemias (folate or B12 deficiencies)
• Intravascular hemolysis (many causes)
  
• Extravascular hemolysis
• Big hematomas
• GI bleeding

• LIVER FAILS TO TAKE UP AND/OR CONJUGATE BILIRUBIN ("hepatocellular jaundice")
• Newborns (don’t give opiates (except meperidine), sulfonamides)
• Hypoperfusion (CHF)
• Bad alcoholism
• Hepatitis (many causes)
• Cirrhosis (many causes)
• Glucuronyl transferase (solubilizes bilirubin)
• Gilbert’s non-disease [worse w/ fasting)
• Crigler-Najjar

• LIVER DOESN'T SEND BILIRUBIN TO THE RIGHT PLACE ("cholestatic jaundice" water soluble so urine can be darker)
• Problems with the liver cells
• Drugs (estrogen, anabolic steroids)
• Dubin-Johnson (pigmented) non-disease
• These people lack a pump
• Rotor (non-pigmented) non-disease.
• Problems with the bile ducts in the liver
• Biliary cirrhosis
• Biliary atresia
• Problems with the bile ducts beyond the liver (surgical)
• Gallstone in the common duct (the only time a gallstone in the gallbladder will cause jaundice is in Mirizzi Syndrome)Cancer (i.e., biliary, pancreatic, ampullary)
• Iatrogenic (i.e., the surgeon nicked the common bile duct)
  

BTW: the eye sclera should never be yellow if the "jaundice" from carrots.

Gram Positive Cocci MindMap

2 for 1 Deal... Ramsay Hunt Syndrome and Bullous Myringitis

The differential of vesicles/bullae in the external ear are Ramsay Hunt Syndrome and bullous myringitis. Ramsay Hunt Syndrome is an extremely painful manifestation of varicella zoster virus and is one of the indications for IV acyclovir. It can also include hyperacusis and loss of taste to the anterior 2/3 of the tongue. Bullous myringitis (image on right) is seen atypical (non-productive cough) pneumonia from mycoplasma.

2 for 1 Deal... Salmonella typhi and Ceftriaxone

Two unusual things "live" in the gallbladder. One is S. typhi, which is a motile gram negative rod who "swims" upstream from the colon to the gallbladder and lives there chronically (see Typhoid Mary). It also famous for causing rose spots on the abdomen and relative bradycardia.

Ceftriaxone is a lipid soluble third generation cephalosporin which is famous for treating a wide variety of diseases including gram negative and gram positives. Since it is lipid soluble it can cross the blood-brain barrier and is useful for the empiric treatment of meningitis. Like most lipid soluble drugs, it is metabolized by the liver and is excreted in the bile. It reaches very high concentrations in the gall bladder where is causes gallbladder sludge.

2 for 1 Deal... Botulinum and Eaton Lambert Syndrome

2 diseases inhibit the release of ACh from the presynaptic terminal. The obvious one is the botulinum toxin. The other disease is Eaton Lambert syndrome which is an autoimmune process in which antibodies develop to the voltage-gated calcium channels and impair the release of ACh from the presynaptic terminal. Eaton Lambert syndrome is often a paraneoplastic syndrome associated with small cell lung cancer.

Myasthenia gravis and Eaton Lambert often appear in the same question. The key difference to look for in the question stem is whether or not the weakness gets better or worse throughout the day. Myasthenia gravis gets worse as the day progresses. Eaton Lambert gets better.

2 for 1 Deal... Idiopathic Thrombocytopenic Purpura and Abciximab

Idiopathic thrombocytopenic purpura and the drug abciximab both target platelet membrane glycoprotein IIb-IIIa. ITP is an immune destruction of platelets. Besides being impossible to pronounce, abciximab is used in patients undergoing percutaneous coronary intervention, and is an antiplatelet agent.

Gluteus maximus, medius, minimus

It is easy to mix up the actions and innervations of the gluteus maximus, gluteus medius, and gluteus minimus. The easiest way to approach questions on the gluteal muscles is to group the gluteus medius and minimus together. The medius and minimus both abduct the hip or more importantly, they allow our hips to stay level when we stand on one leg (Trendelenburg Test). The gluteus maximus helps us get out of a chair. The trick to these muscles is their innervation. The maximus goes with the inferior gluteal nerve. The medius and minimus are both innervated by the superior gluteal nerve. Be aware of this because it would seem logical that the maximus would go with the superior, but it doesn't!

2 for 1 deal... Achalasia and Hirschsprung's Disease

Achalasia is the Hirschsprung's of the esophagus. Both are missing the Auerbach's plexus (or myenteric plexus). Both have problems relaxing. Achalasia causes a megaesophagus and Hischsprung's causes a mega colon.

Note that Chagas disease = achalasia + Hirschsprung's. Chagas disease can cause both a megaesophagus and a megacolon.