Medical Books, USMLE
2013 First Aid for the USMLE Step 1
Official Updates, Corrections, and Clarifications
Final Dec. 31, 2013
Despite our best efforts, errors do occur during a revision. This update addresses content errors and typos that may create confusion. If you are the first to submit a referenced correction or suggestion to us at www.firstaidteam.com that we accept and integrate into the book, you will receive up to a $20 gift certificate. We check every submission against your reference or other authoritative references to ensure accuracy. Please note that our goal is to provide a high-yield framework for studying and not a comprehensive textbook. Good luck with your studies!
–The First Aid/USMLE-Rx Team
CATEGORIES OF UPDATES
? Factual errors that interfere with comprehension
? Less significant errors that may cause confusion
Suggestions & Clarifications
? The text is accurate, but could be written more clearly
? Minor formatting issues (misalignments, indents, etc.)
? Helpful additions that improve the quality of a fact
In the figure depicting tRNA charging, methionine should not be included on the left image. Amino acids such as methionine are covalently bound to the 3? end of the tRNA by aminoacyl-tRNA synthetases.
Vitamin B1 (thiamine)
In the first mnemonic in column 3, the three enzymes are not required for ATP synthesis. Thus please replace the mnemonic with: “Think ATP: ?-ketoglutarate dehydrogenase, Transketolase, and Pyruvate dehydrogenase.”
Vitamin B3 (niacin)
The synthesis of vitamin B3 (niacin) requires both vitamin B6 (pyridoxine) and vitamin B2 (riboflavin).
Electron transport chain and oxidative phosphorylation
The arrow beneath “Complex V” should be facing upward (to reflect movement of protons through the complex), not downward.
Lysosomal storage diseases
In the entry for Krabbe’s disease, in the fourth column, add psychosine as an accumulated substrate.
The chemical composition of the plasma membrane is best described as a phospholipid bilayer, not a lipoprotein bilayer.
Please remove Bacillus from the list of examples, since some species are strict aerobes while others are facultative anaerobes.
(1) In the entry for EIEC, in the second column, delete “No toxins
(2) In the entry for ETEC, replace the first sentence with: “Produces
heat-labile and heat-stable enteroToxins.”
(3) In the entry for EHEC, the mechanism is better explains as follows:
“Microthrombi form on endothelium damaged by toxin ? mechanical
hemolysis (schistocytes formed) and ? renal blood flow; microthrombi
consume platelets ? thrombocytopenia.”
Salmonella vs. Shigella
In the fifth row, note that antibiotic therapy may prolong fecal excretion of Salmonella, and shorten the duration of fecal excretion of Shigella.
(1) In the entry for Enterobium vermicularis, note that transmission is via
the fecal-oral route.
(2) In the entry for Toxocara canis, note that transmission is via the
For the hepatitis D virus (HDV) entry, in the incubation column, note that co-infection represents an acute infection of both HBV and HDV and superinfection represents infection with HDV after developing chronic HBV.
Ticarcillin, piperacillin (antipseudomonals)
In the entry for Clinical use, replace “use with clavulanic acid.” with “use with ?-lactamase inhibitors.”
In the entry for Mechanism, replace “(transpeptidation)” with “(translocation).”
Replace the entry for Toxicity with: “GI upset, headaches, hepatoxicity, taste disturbances.”
Tumor suppressor genes
BRAF is a proto-oncogene, not a tumor suppressor gene.
G-protein–linked 2nd messengers
For the Gq-coupled receptor pathway, note that the role of phospholipase C is not to cleave lipids into PIP2, but rather to cleave PIP2 into both DAG and IP3 (one step downstream).
Cardiac and vascular function curves
For the graph, note that an acute, uncompensated hemorrhage would result in a left shift of the volume curve; cardiac function would not be affected. See the new position of below:
Please delete cardiac tamponade.
(1) In the entry for regulation, note that growth hormone (GH) increases insulin resistance, leading indirectly to increased insulin secretion. It does not directly stimulate insulin release.
(2) Under the list of insulin regulators, note that ?2-agonists, not antagonists, increase insulin secretion.
(3) In the image of a pancreatic ? cell, note that glucose enters the cell via GLUT-4, not GLUT-1.
In the entry for trypsinogen, replace “creation of more trypsinogen” with “cleaving of additional trypsinogen molecules into active trypsin (positive feedback loop).”
Note that NSAIDs decrease PGE2, not PGE1.
Molecular pathogenesis of CRC
Note that the APC/?-catenin pathway leads to sporadic cancer.
In the entry for pigmented stones, note that black stones are radiopaque and associated with hemolysis, while brown stones are radiolucent and associated with infection.
Pathologic RBC forms
In the entry for acanthocytes (spur cells), the image shown is actually an echinocyte (burr cell). Acanthocytes have irregularly spaced, longer projections (see image below) as compared to burr cells, whose projections are smaller and more uniformly spaced.
Image: This image is a derivative work, adapted from the following source, under the Creative Commons Attribution license: courtesy of Dr. Ed Uthman.
Other RBC pathologies
Under the entry for Heinz bodies, note that the mechanism for Heinz body formation is oxidation of hemoglobin sulfhydryl groups leading to denatured hemoglobin precipitation.
It is the lymphocyte-rich variant of Hodgkin’s lymphoma that has the best long-term prognosis, not the nodular sclerosing form.
In the entry for chronic myelogenous leukemia, please replace the second paragraph with: “Very low leukocyte alkaline phosphatase (LAP) as a result of low activity in mature granulocytes (vs. leukemoid reaction, in which LAP is increased).”
Ischemic brain disease/stroke
The definition of a transient ischemic attack is a brief, reversible episode of focal neurological dysfunction lasting < 24 hours without acute infarction (negative MRI). The majority of TIAs resolve in <15 minutes.
Spinal cord and associated tracts
The lateral spinothalamic tract label should be posterior and lateral to the anterior spinothalamic tract, as opposed to indicating the dorsal horn.
For the components of a complete hydatidiform mole, replace "2 sperm + empty egg" with “Enucleated egg + single sperm (subsequently duplicates paternal DNA); empty egg + 2 sperm is rare.”
(1) For the Histone methylation entry, in column 2, replace “Inactivates
transcription of DNA.” with “Usually reversibly represses DNA
transcription, but can activate it in some cases.” And in column 3
replace “Methylation makes DNA Mute.” with “Histone Methylation
Mostly Makes DNA Mute.”
(2) For the DNA methylation entry, add to the end of column 2 that “DNA
methylation at CpG islands represses transcription.” And in column 3
add: “CpG Methylation Makes DNA Mute.”
(3) For the Histone acetylation entry, revise the mnemonic to add the
word Histone: “Histone Acetylation makes DNA Active.”
In the entry for DNA ligase, please replace “phosphodiesterase” with “phosphodiester.”
(1) In the entry for Initiation, in the second column, replace “Activated”
(2) In the entry for Termination, in the second column, replace “protein”
For the type III entry, replace the phrase in column 3 as follows: Type III: deficient in the uncommon, vascular type of Ehlers-Danlos syndrome (ThreE D).
In the second paragraph, please note that in the most common type of OI (type I), the mutation leads to decreased production of otherwise normal type I collagen.
In the entry for Down syndrome, the last sentence of the third column should read, “Ultrasound in first trimester shows ? nuchal translucency.”
In the entry for Function, in the last column, change “Necessary for the synthesis of clotting factors…” to “Necessary for the activation of clotting factors…”
Disorders of galactose metabolism
In the drawing, in the lower right, replace “Glycolysis/Gluconeogenesis” with “Glycolysis/glycogenesis.”
Fatty acid metabolism
Replace the label “Inner mitochondrial membrane” with “Mitochondrial membranes.”
Note that an associated symptom is conjunctival suffusion, not conjunctivitis.
In the entry for Toxoplasma gondii, in the Transmission column, replace the first part of the first sentence with: “Cysts in meat or oocysts in cat feces.”
Please revise the transmission of Trypanosoma cruzi as follows: “Reduviid bug feces (“kissing bug”), deposited in a painless bite (much like a kiss).”
The correct spelling is lumefantrine.
Sinusoids of spleen
Infections in immunodeficiency
For these two facts, please add E. coli to the list of encapsulated organisms and change the mnemonic to “SHiNE SkiS” (the E is for E. coli).
Interatrial septum development
In the text for step 5, note that the septum secundum, not the foramen secundum, enlarges.
Signaling pathways of endocrine hormones
To clarify, the IP3 pathway plays a minor role in GHRH signaling. The principal signaling pathway for GHRH is cAMP accumulation.
(1) In the last column, please replace “Duodenum (2nd and 3rd parts)”
with “Duodenum (2nd through 4th parts)”
(2) In the last column, please replace “Rectum (lower 2/3)” with “Rectum
Please remove the leader line and label for deep inguinal ring.
Intussusception and volvulus
Note that intussusception can be associated with recent enteric or respiratory viral infections.
Other intestinal disorders
In the entry for ischemic colitis, note that pain out of proportion with physical findings is more associated with acute mesenteric ischemia,
Serum markers of liver and pancreas pathology
In the entry for ?-glutamyl transpeptidase, note that GGT is also a marker of alcohol use.
Langerhans cell histiocytosis
Delete “(neural crest origin)” from the second-to-last sentence of the second paragraph. Langerhans cells are of mesodermal origin, despite expressing the marker S-100.
In the entry for treatment, colchicine is also used to treat acute gout.
Please note that colchicine is primarily used clinically to treat acute gout rather than chronic gout.
In the entry for output, note that the output nerves are Purkinje cells, not Purkinje fibers.
Wilms’ tumor (nephroblastoma)
In the third column, replace “WT1” with “WT1 or WT2.”
Acute renal failure (acute kidney injury)
In the table, the postrenal FENa will be >1% in mild disease and >2% in severe disease.
The urethra is derived mostly from endoderm, not mesoderm.
The arrow indicating when ovulation occurs should appear slightly after the LH surge, rather than before the LH surge.
Lung cancer (continued)
Mesothelioma is not a lung cancer per se, but rather a malignancy of the pleura.
The treatment for Sporothrix schenckii should be oral potassium iodide, not potassium chloride.
SUGGESTIONS & CLARIFICATIONS
Authoritative references for the duration of grief and pathologic grief vary substantially. The best definition appears to be that normal grief can last up to 6-12 months, while pathologic grief lasts longer. Associated characteristics (e.g., intensity of grief, delusions) can help differentiate between the two.
De novo pyrimidine and purine synthesis
This fact states that “Various antineoplastic and antibiotic drugs function by interfering with purine synthesis.” Please note that some of the drugs listed interfere with purine synthesis, while others interfere with pyrimidine synthesis.
Replace the sentence in column 3 with: “Classical type (joint and skin symptoms): caused by a mutation in type V collagen.”
Replace “Most common form is X-linked recessive” with “Most common form is X-linked; males are more severely affected than female carriers.”
In the entry for Imprinting, replace the word “mutation” with “allele.”
(1) For Prader-Willi syndrome, change “Paternal allele is not expressed” to “Gene from mom is normally silent and Paternal gene is deleted/mutated.”
(2) For Angelman syndrome, change “Maternal allele is not expressed” to “Gene from dad is normally silent and Matenal gene is deleted/ mutated.”
In the entry for hereditary spherocytosis, note that splenectomy is the treatment, but it does not cure the condition.
Summary of pathways
For the vitamin B12-dependent succinyl-CoA synthesis pathway, replace “Odd-chain fatty acids and branched-chain amino acids” with “Odd-chain fatty acids, branched-chain amino acids, methionine, and threonine.”
Glycolysis regulation, key enzymes
Under the box for glycolysis steps requiring ATP, replace “*Glucokinase in liver; hexokinase in all other tissues.” With “*Glucokinase in liver and ? cells of pancreas; hexokinase in all other tissues.”
TCA cycle (Krebs cycle)
The calculation of 10 ATP produced per acetyl-CoA via the TCA cycle is based on 2.5 ATP per NADH, 1.5 ATP per FADH2, and 1 ATP per GTP.
Electron transport chain and oxidative phosphorylation
In the entry for ATP produced via ATP synthase, replace “1 NADH ? 3 ATP; 1 FADH2 ? 2 ATP.” With “1 NADH ? 2.5 ATP; 1 FADH2 ? 1.5 ATP.”
Respiratory burst (oxidative burst)
In the last line, replace “because they neutralize” to “capable of neutralizing.”
Note that levels of sorbitol dehydrogenase in the lens of the eye, while present, are much lower than in the other tissue types listed.
(1) In three instances (once in text, once in the main drawing, and once
in the boxed drawing), replace “NH4” with “NH3.”
(2) In the main drawing, the blue area indicating mitochondria should
extend to include half of citrulline and ornithine, to more clearly
indicate that ornithine is formed in the cytoplasm, passes from the
cytoplasm to the mitochondrial matrix, and is carbamylated; the
resulting citrulline passes from the mitochondrial matrix to the
Transport of ammonium by alanine and glutamate
In the Fact title, replace “ammonium” with “ammonia.”
Catecholamine synthesis/tyrosine catabolism
For the box labeled “Breakdown products via MAO and COMT,” update the contents as follows:
??Dopamine ? HVA
??Norepinephrine ? Normetanephrine ? VMA
??Epinephrine ? Metanephrine ? VMA
In the last entry in the third column, delete the parenthetical information “(favored by high redox state).”
Pseudomonas aeruginosa may use some nitrogen-containing compounds (e.g., nitrates) as terminal electron acceptors for anaerobic metabolism in environments with low or absent oxygen.
Gram-negative lab algorithm
Since Helicobacter pylori is comma shaped, it can be moved from the bottom of the algorithm to the top right:
Lactose-fermenting enteric bacteria
Note that Serratia is a weak fermenter of lactose.
In the entry for Cryptosporidium, the disease is transmitted via oocysts (not cysts) in water.
Since picornavirus is an RNA virus and parvovirus is a DNA virus, the mnemonic makes more sense if the order of picornavirus and parvovirus is switched in the second column.
In the entry for Poxvirus, in the last column, delete the word “Vaccinia.” The line should read: Cowpox (“milkmaid blisters”).
Common diseases of HIV-positive adults
In the entry for Pneumonia, in the second column, another characteristic finding is a ground glass appearance on imaging.
In the entry for Clinical use, delete “and syphilis” (redundant with T. pallidum).
Ampicillin, amoxicillin (aminopenicillins)
In the entry for Toxicity, delete the word “ampicillin” so the text reads simply “rash.”
In the entry for migration, under the second column, replace “Bacterial products” with “Chemotactic products released in response to bacteria.”
Under the entry for MIs as an application of ?-blockers, note that the specific agents shown to reduce mortality (per the COMET trial) are metoprolol, carvedilol, and bisoprolol.
Auscultation of the heart
Please refer to the updated heart murmurs chart shown below:
(1) For the description of the aortic stenosis murmur, replace “Radiates to carotids/heart base” with “Loudest at heart base; radiates to carotids.”
(2) In the entry for mitral valve prolapse, replace “Loudest at S2” with “Loudest just before S2.”
(3) In the entry for mitral valve prolapse, replace “Enhanced by maneuvers…” with “Occurs earlier with maneuvers…”
In the entry for ezetimibe, regarding its mechanism of action, replace “reabsorption” with “absorption.”
Hypothyroidism vs. hyperthyroidism
Myxedema (facial/periorbital) is correctly listed as associated with hypothyroidism. Note, however, that periorbital edema is also associated with hyperthyroidism.
(1) In the entry for acute manifestations, in the second column, add “can be caused by” before the “unopposed secretion of GH” (diabetes does not cause unopposed secretion of GH).
(2) In the entry for chronic manifestations, in the second paragraph, replace “(sorbitol accumulation in organs with aldose reductase)” with “(sorbitol accumulation in organs with aldose reductase and decreased or absent sorbitol dehydrogenase).”
(3) In the entry for chronic manifestations, in the first bullet point, replace “arteriosclerosis leading to hypertension” with “arteriolosclerosis leading to hypertension,” which better reflects the small vessel nature of the disease process.
Multiple endocrine neoplasias (MEN)
Please note that MEN 2A is associated with parathyroid hyperplasia, not parathyroid tumors.
To the end of the first paragraph, add “of bile synthesis,” so that the sentence reads: “Cholesterol 7?-hydroxylase catalyzes rate-limiting step of bile synthesis.”
In the entry for Boerhaave syndrome, note that the transmural rupture is typically of the distal esophagus.
Replace “? mucosal absorption that primarily affects jejunum” with
“? mucosal absorption that primarily affects distal duodenum and/or proximal jejunum.”
In the entry for Gilbert’s syndrome, in the second column, replace the first sentence with the following: “Mildly ? UDP-glucuronyl transferase conjugation activity leading to ? bilirubin uptake by hepatocytes.”
Microcytic, hypochromic (MCV < 80 fL) anemia
(1) In the entry for ?-thalassemia, first sentence of second column, replace “?-globin gene mutations” with “?-globin gene deletions” to better reflect the genetic defect.
(2) In the third column, replace all instances of “gene” with “allele.”
Extrinsic hemolytic normocytic anemia
(1) For the indirect Coombs’ test, to trigger the reaction, anti-IgG antibodies (Coombs’ reagent) must be added after the RBCs are added to the patient’s serum.
(2) For the direct Coombs’ test, note that anti-Ig antibodies are added to the patient’s blood, not serum.
Hereditary thrombosis syndromes leading to hypercoagulability
For antithrombin deficiency, please replace “? in PTT is blunted after heparin administration” with “has no direct effect on PT, PTT, or thrombin time but diminishes the increase in PTT following heparin administration.”
Chronic myeloproliferative disorders
In the entry for polycythemia vera, please replace “constitutively active JAK2 receptors” with “constitutively active JAK-STAT signaling pathway” (JAK2 is a non-receptor tyrosine kinase).
In the entry for toxicity, note that overdose causes respiratory alkalosis initially, which is then superimposed by metabolic acidosis.
In the entry for azathioprine, 6-MP, and 6-TG, for toxicities: note that only azathioprine and 6-MP (but not 6-TG) are metabolized by xanthine oxidase; thus both have increased toxicity with allopurinol, which inhibits their metabolism.
Upper extremity nerves
For the median nerve territory, please replace “(C5–C8, T1)” with “C5-T1”).
In the homunculus image, we do not show the sensory distribution of the abdomen and genitalia.
Effects of strokes
With a PICA (lateral medullary) stroke, in the column for symptoms, there is decreased pain and temperature sensation from the ipsilateral face and the contralateral body.
In the diagram, remove the arrows associated with the green lines that point toward the cerebral cortex; CN VII is predominantly efferent.
Common eye conditions
Accommodation is not an eye condition, but rather a normal physiological function to focus on near objects.
Extraocular muscles and nerves
In the entry for CN IV damage, replace “ipsilateral head tilt” with “head tilt toward the side of the lesion.”
Sturge-Weber syndrome can also be associated with hemiplegia.
In the third column, angiotensin II receptor blockers have a reduced (rather than absent) risk of cough/angioedema.
Female reproductive epithelial histology
Note that the stratified squamous epithelium of the ectocervix is also nonkeratinized.
In the line drawing, the size of primary spermatocytes is generally equal to that of spermatogonia, not smaller.
Replace the third sentence of the second column with the following: “Associated with HPV 16 and HPV 18, which produce both the E6 gene product (inhibits p53 suppressor gene) and E7 gene product (inhibits RB suppressor gene).”
In the third column, the spelling of “esophagus” should be changed to “oesophagus” to make the mnemonic for “10 letters at T10” valid.
In the entry for methylxanthines, replace “thereby ? cAMP hydrolysis” with “thereby resulting in ? cAMP levels due to ? cAMP hydrolysis.”
Download USMLE Step 1 Errata
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