Clinical Reasoning

Clinical Reasoning US Medical PG Question 1: A group of neurologists develop a new blood test for Alzheimer's. They are optimistic about the test, as they have found that for any given patient, the test repeatedly produces very similar results. However, they find that the new test results are not necessarily consistent with the gold standard of diagnosis. How would this new test most accurately be described?

• A. Valid and reliable
• B. Reliable (Correct Answer)
• C. Valid
• D. Biased
• E. Neither valid nor reliable

Clinical Reasoning Explanation: ***Reliable*** - The test produces **similar results repeatedly** upon repeated measures, indicating high **reliability** or **precision**. - Reliability refers to the **consistency** of a measure, even if it is not accurate. *Valid and reliable* - While the test is **reliable**, it is explicitly stated that the results are **not consistent with the gold standard**, meaning it lacks **validity**. - A test must be both **consistent** (reliable) and **accurate** (valid) to be described as valid and reliable. *Valid* - **Validity** refers to the **accuracy** of a test, or how well it measures what it is supposed to measure. - The test is explicitly stated to **not be consistent with the gold standard**, indicating a lack of agreement with the true measure of Alzheimer's. *Biased* - **Bias** refers to a **systematic error** in measurement that can lead to consistently high or low results compared to the true value. - While the test might be biased due to its lack of consistency with the gold standard, "biased" is not the most accurate single descriptor of its measurement properties given the information provided. *Neither valid nor reliable* - The test is described as producing **very similar results repeatedly**, which directly indicates it has **high reliability**. - Therefore, stating it is neither valid nor reliable is incorrect, as it possesses reliability.

Clinical Reasoning US Medical PG Question 2: A 25-year-old man with a genetic disorder presents for genetic counseling because he is concerned about the risk that any children he has will have the same disease as himself. Specifically, since childhood he has had difficulty breathing requiring bronchodilators, inhaled corticosteroids, and chest physiotherapy. He has also had diarrhea and malabsorption requiring enzyme replacement therapy. If his wife comes from a population where 1 in 10,000 people are affected by this same disorder, which of the following best represents the likelihood a child would be affected as well?

• A. 0.01%
• B. 2%
• C. 0.5%
• D. 1% (Correct Answer)
• E. 50%

Clinical Reasoning Explanation: ***Correct Option: 1%*** - The patient's symptoms (difficulty breathing requiring bronchodilators, inhaled corticosteroids, and chest physiotherapy; diarrhea and malabsorption requiring enzyme replacement therapy) are classic for **cystic fibrosis (CF)**, an **autosomal recessive disorder**. - For an autosomal recessive disorder with a prevalence of 1 in 10,000 in the general population, **q² = 1/10,000**, so **q = 1/100 = 0.01**. The carrier frequency **(2pq)** is approximately **2q = 2 × (1/100) = 1/50 = 0.02**. - The affected man is **homozygous recessive (aa)** and will always pass on the recessive allele. His wife has a **1/50 chance of being a carrier (Aa)**. If she is a carrier, she has a **1/2 chance of passing on the recessive allele**. - Therefore, the probability of an affected child = **(Probability wife is a carrier) × (Probability wife passes recessive allele) = 1/50 × 1/2 = 1/100 = 1%**. *Incorrect Option: 0.01%* - This percentage is too low and does not correctly account for the carrier frequency in the population and the probability of transmission from a carrier mother. *Incorrect Option: 2%* - This represents approximately the carrier frequency (1/50 ≈ 2%), but does not account for the additional 1/2 probability that a carrier mother would pass on the recessive allele. *Incorrect Option: 0.5%* - This value would be correct if the carrier frequency were 1/100 instead of 1/50, which does not match the given population prevalence. *Incorrect Option: 50%* - **50%** would be the risk if both parents were carriers of an autosomal recessive disorder (1/4 chance = 25% for affected, but if we know one parent passes the allele, conditional probability changes). More accurately, 50% would apply if the disorder were **autosomal dominant** with one affected parent, which is not the case here.

Clinical Reasoning US Medical PG Question 3: A 26-year-old medical student comes to the physician with a 3-week history of night sweats and myalgias. During this time, he has also had a 3.6-kg (8-lb) weight loss. He returned from a 6-month tropical medicine rotation in Cambodia 1 month ago. A chest x-ray (CXR) shows reticulonodular opacities suggestive of active tuberculosis (TB). The student is curious about his likelihood of having active TB. He reads a study that compares sputum testing results between 2,800 patients with likely active TB on a basis of history, clinical symptoms, and CXR pattern and 2,400 controls. The results are shown: Sputum testing positive for TB Sputum testing negative for TB Total Active TB likely on basis of history, clinical symptoms, and CXR pattern 700 2100 2,800 Active TB not likely on basis of history, clinical symptoms, and CXR pattern 300 2100 2,400 Total 1000 4200 5,200 Which of the following values reflects the probability that a patient with a diagnosis of active TB on the basis of history, clinical symptoms, and CXR pattern actually has active TB?

• A. 1.4
• B. 0.50
• C. 0.70
• D. 0.88
• E. 0.25 (Correct Answer)

Clinical Reasoning Explanation: ***0.25*** - This value represents the **positive predictive value (PPV)** for active TB based on the initial clinical assessment criteria (history, symptoms, CXR). - PPV is calculated as the number of true positives (700) divided by the total number of individuals with a positive clinical diagnosis (700 + 2100 = 2800). So, 700 / 2800 = 0.25. - **This answers the question**: the probability that someone with a clinical diagnosis of active TB actually has the disease. *Incorrect 1.4* - This value is not a valid probability, as probabilities must be between 0 and 1.0. - It might arise from an incorrect calculation or misinterpretation of the provided data. *Incorrect 0.50* - This value does not correspond to any standard diagnostic metric calculated from the provided data. - The actual prevalence of TB (based on positive sputum) is 1000/5200 = 0.19, not 0.50. - This is likely a distractor with no meaningful interpretation in this context. *Incorrect 0.70* - This value represents the **sensitivity** of the sputum test for detecting active TB. - Sensitivity is calculated as true positives (700) divided by total with disease (700 + 300 = 1000). So, 700 / 1000 = 0.70. - Sensitivity tells us how good the test is at detecting disease when present, not the probability of having disease given a positive clinical diagnosis. *Incorrect 0.88* - This value represents the **specificity** of the clinical assessment. - Specificity is calculated as true negatives (2100) divided by total without disease (2100 + 300 = 2400). So, 2100 / 2400 = 0.875 ≈ 0.88. - Specificity tells us how good the assessment is at ruling out disease in those without it, not the probability of disease given a positive assessment.

Clinical Reasoning US Medical PG Question 4: A scientist in Boston is studying a new blood test to detect Ab to the parainfluenza virus with increased sensitivity and specificity. So far, her best attempt at creating such an exam reached 82% sensitivity and 88% specificity. She is hoping to increase these numbers by at least 2 percent for each value. After several years of work, she believes that she has actually managed to reach a sensitivity and specificity even greater than what she had originally hoped for. She travels to South America to begin testing her newest blood test. She finds 2,000 patients who are willing to participate in her study. Of the 2,000 patients, 1,200 of them are known to be infected with the parainfluenza virus. The scientist tests these 1,200 patients’ blood and finds that only 120 of them tested negative with her new test. Of the following options, which describes the sensitivity of the test?

• A. 82%
• B. 86%
• C. 98%
• D. 90% (Correct Answer)
• E. 84%

Clinical Reasoning Explanation: ***90%*** - **Sensitivity** is calculated as the number of **true positives** divided by the total number of individuals with the disease (true positives + false negatives). - In this scenario, there were 1200 infected patients (total diseased), and 120 of them tested negative (false negatives). Therefore, 1200 - 120 = 1080 patients tested positive (true positives). The sensitivity is 1080 / 1200 = 0.90, or **90%**. *82%* - This value was the **original sensitivity** of the test before the scientist improved it. - The question states that the scientist believes she has achieved a sensitivity "even greater than what she had originally hoped for." *86%* - This value is not directly derivable from the given data for the new test's sensitivity. - It might represent an intermediate calculation or an incorrect interpretation of the provided numbers. *98%* - This would imply only 24 false negatives out of 1200 true disease cases, which is not the case (120 false negatives). - A sensitivity of 98% would be significantly higher than the calculated 90% and the initial stated values. *84%* - This value is not derived from the presented data regarding the new test's performance. - It could be mistaken for an attempt to add 2% to the original 82% sensitivity, but the actual data from the new test should be used.

Clinical Reasoning US Medical PG Question 5: A geriatric investigator is evaluating the consistency of Alzheimer dementia diagnoses based on clinical symptoms. Patients with known chart diagnoses of Alzheimer dementia were evaluated by multiple physicians during a fixed time interval. Each evaluator was blinded to the others' assessments. The extent to which the diagnosis by one physician was replicated by another clinician examining the same patient is best described by which of the following terms?

• A. Validity
• B. Specificity
• C. Predictive value
• D. Sensitivity
• E. Precision (Correct Answer)

Clinical Reasoning Explanation: ***Precision*** - **Precision** refers to the consistency or reproducibility of a measurement or diagnosis. When multiple physicians reach the same diagnosis for the same patient, it indicates high precision. - In this context, it specifically assesses **inter-rater reliability**, which is the extent to which different observers agree on the same assessment. *Validity* - **Validity** refers to the extent to which a test or measure accurately assesses what it is intended to measure. It is about the "truthfulness" of the diagnosis. - While important for diagnosis, validity is about accuracy against a gold standard, not consistency among different observers. *Specificity* - **Specificity** is the ability of a test to correctly identify individuals who do *not* have the disease (true negatives). - It measures the proportion of healthy individuals who are correctly identified as healthy by the test, which is not what is being evaluated here. *Predictive value* - **Predictive value** assesses the probability that a person *actually has* (positive predictive value) or *does not have* (negative predictive value) a disease given their test result. - This concept relates to the diagnostic utility of a test in a population, not the consistency of different clinician diagnoses. *Sensitivity* - **Sensitivity** is the ability of a test to correctly identify individuals who *do* have the disease (true positives). - It measures the proportion of diseased individuals who are correctly identified as diseased by the test, which is distinct from inter-rater agreement.

Clinical Reasoning US Medical PG Question 6: You are reading through a recent article that reports significant decreases in all-cause mortality for patients with malignant melanoma following treatment with a novel biological infusion. Which of the following choices refers to the probability that a study will find a statistically significant difference when one truly does exist?

• A. Type II error
• B. Type I error
• C. Confidence interval
• D. p-value
• E. Power (Correct Answer)

Clinical Reasoning Explanation: ***Power*** - **Power** is the probability that a study will correctly reject the null hypothesis when it is, in fact, false (i.e., will find a statistically significant difference when one truly exists). - A study with high power minimizes the risk of a **Type II error** (failing to detect a real effect). *Type II error* - A **Type II error** (or **beta error**) occurs when a study fails to reject a false null hypothesis, meaning it concludes there is no significant difference when one actually exists. - This is the **opposite** of what the question describes, which asks for the probability of *finding* a difference. *Type I error* - A **Type I error** (or **alpha error**) occurs when a study incorrectly rejects a true null hypothesis, concluding there is a significant difference when one does not actually exist. - This relates to the **p-value** and the level of statistical significance (e.g., p < 0.05). *Confidence interval* - A **confidence interval** provides a range of values within which the true population parameter is likely to lie with a certain degree of confidence (e.g., 95%). - It does not directly represent the probability of finding a statistically significant difference when one truly exists. *p-value* - The **p-value** is the probability of observing data as extreme as, or more extreme than, that obtained in the study, assuming the null hypothesis is true. - It is used to determine statistical significance, but it is not the probability of detecting a true effect.

Clinical Reasoning US Medical PG Question 7: A 55-year-old woman presents with fatigue and flu-like symptoms. She says her symptoms started 5 days ago with a low-grade fever and myalgia, which have not improved. For the past 4 days, she has also had chills, sore throat, and rhinorrhea. She works as a kindergarten teacher and says several children in her class have had similar symptoms. Her past medical history is significant for depression managed with escitalopram, and dysmenorrhea. A review of systems is significant for general fatigue for the past 5 months. Her vital signs include: temperature 38.5°C (101.3°F), pulse 99/min, blood pressure 115/75 mm Hg, and respiratory rate 22/min. Physical examination reveals pallor of the mucous membranes. Initial laboratory findings are significant for the following: Hematocrit 24.5% Hemoglobin 11.0 g/dL Platelet Count 215,000/mm3 Mean corpuscular volume (MCV) 82 fL Red cell distribution width (RDW) 10.5% Which of the following is the best next diagnostic test in this patient?

• A. Serum iron level
• B. Serum ferritin level
• C. Reticulocyte count (Correct Answer)
• D. Hemoglobin electrophoresis
• E. Serum folate level

Clinical Reasoning Explanation: ***Reticulocyte count*** - The patient presents with **fatigue, pallor, and anemia (Hb 11.0 g/dL)**. Given the acute illness (flu-like symptoms) and underlying chronic fatigue, a **reticulocyte count** helps determine if the bone marrow is adequately responding to the anemia. - A low or inappropriately normal reticulocyte count in the setting of anemia suggests a problem with **red blood cell production** (e.g., marrow suppression, nutritional deficiency), while a high count would suggest hemolysis or acute blood loss. *Serum iron level* - While iron-deficiency anemia is common, the patient's **MCV of 82 fL** is within the normal range, suggesting a **normocytic anemia**, which makes iron deficiency less likely as a primary cause without further investigation. - Furthermore, **serum iron levels** can be acutely affected by inflammation or infection, making them unreliable in the presence of acute flu-like symptoms. *Serum ferritin level* - **Ferritin** is an acute-phase reactant; therefore, in the context of an acute infection or inflammation (flu-like symptoms, fever), a **serum ferritin level** can be falsely elevated, masking true iron deficiency, which makes it less reliable as the *best first* diagnostic test in this scenario. - While low ferritin is diagnostic of iron deficiency, a normal or even elevated ferritin does not rule it out in the presence of inflammation, thus complicating interpretation. *Hemoglobin electrophoresis* - **Hemoglobin electrophoresis** is used to diagnose **hemoglobinopathies** like **sickle cell disease** or **thalassemia**. There are no clinical or laboratory findings (e.g., microcytosis, prior family history of hemoglobinopathies) to suggest this as the most appropriate initial investigation for this patient's acute presentation. - The patient's **normocytic anemia** (MCV 82 fL) further argues against typical thalassemia presentations, which are usually microcytic. *Serum folate level* - **Folate deficiency** typically causes a **macrocytic anemia** (elevated MCV), which is not observed in this patient (MCV 82 fL being normocytic). - There are no specific risk factors or clinical signs presented that would clearly point towards folate deficiency as the primary cause for her anemia.

Clinical Reasoning US Medical PG Question 8: A research group wants to assess the safety and toxicity profile of a new drug. A clinical trial is conducted with 20 volunteers to estimate the maximum tolerated dose and monitor the apparent toxicity of the drug. The study design is best described as which of the following phases of a clinical trial?

• A. Phase 0
• B. Phase III
• C. Phase V
• D. Phase II
• E. Phase I (Correct Answer)

Clinical Reasoning Explanation: ***Phase I*** - **Phase I clinical trials** involve a small group of healthy volunteers (typically 20-100) to primarily assess **drug safety**, determine a safe dosage range, and identify side effects. - The main goal is to establish the **maximum tolerated dose (MTD)** and evaluate the drug's pharmacokinetic and pharmacodynamic profiles. *Phase 0* - **Phase 0 trials** are exploratory studies conducted in a very small number of subjects (10-15) to gather preliminary data on a drug's **pharmacodynamics and pharmacokinetics** in humans. - They involve microdoses, not intended to have therapeutic effects, and thus cannot determine toxicity or MTD. *Phase III* - **Phase III trials** are large-scale studies involving hundreds to thousands of patients to confirm the drug's **efficacy**, monitor side effects, compare it to standard treatments, and collect information that will allow the drug to be used safely. - These trials are conducted after safety and initial efficacy have been established in earlier phases. *Phase V* - "Phase V" is not a standard, recognized phase in the traditional clinical trial classification (Phase 0, I, II, III, IV). - This term might be used in some non-standard research contexts or for post-marketing studies that go beyond Phase IV surveillance, but it is not a formal phase for initial drug development. *Phase II* - **Phase II trials** involve several hundred patients with the condition the drug is intended to treat, focusing on **drug efficacy** and further evaluating safety. - While safety is still monitored, the primary objective shifts to determining if the drug works for its intended purpose and at what dose.

Clinical Reasoning US Medical PG Question 9: An epidemiologist is evaluating the efficacy of Noxbinle in preventing HCC deaths at the population level. A clinical trial shows that over 5 years, the mortality rate from HCC was 25% in the control group and 15% in patients treated with Noxbinle 100 mg daily. Based on this data, how many patients need to be treated with Noxbinle 100 mg to prevent, on average, one death from HCC?

• A. 20
• B. 73
• C. 10 (Correct Answer)
• D. 50
• E. 100

Clinical Reasoning Explanation: ***10*** - The **number needed to treat (NNT)** is calculated by first finding the **absolute risk reduction (ARR)**. - **ARR** = Risk in control group - Risk in treatment group = 25% - 15% = **10%** (or 0.10). - **NNT = 1 / ARR** = 1 / 0.10 = **10 patients**. - This means that **10 patients must be treated with Noxbinle to prevent one death from HCC** over 5 years. *20* - This would result from an ARR of 5% (1/0.05 = 20), which is not supported by the data. - May arise from miscalculating the risk difference or incorrectly halving the actual ARR. *73* - This value does not correspond to any standard calculation of NNT from the given mortality rates. - May result from confusion with other epidemiological measures or calculation error. *50* - This would correspond to an ARR of 2% (1/0.02 = 50), which significantly underestimates the actual risk reduction. - Could result from incorrectly calculating the difference as a proportion rather than absolute percentage points. *100* - This would correspond to an ARR of 1% (1/0.01 = 100), grossly underestimating the treatment benefit. - May result from confusing ARR with relative risk reduction or other calculation errors.

Clinical Reasoning US Medical PG Question 10: A 15-year-old boy is referred to a child psychologist because of worsening behavior and constant disruption in class. He has received multiple reprimands in the past 6 months for not doing the homework his teacher assigned, and he refuses to listen to the classroom instructions. Additionally, his teachers say he is very argumentative and blames other children for not letting him do his work. He was previously well behaved and one of the top students in his class. He denies any recent major life events or changes at home. His past medical history is noncontributory. His vital signs are all within normal limits. Which of the following is the most likely diagnosis?

• A. Attention deficit hyperactivity disorder
• B. Antisocial personality disorder
• C. Conduct disorder
• D. Oppositional defiant disorder (Correct Answer)
• E. Major depressive disorder

Clinical Reasoning Explanation: ***Oppositional defiant disorder*** - This patient's symptoms of **argumentativeness**, **defiance**, and **blaming others**, combined with his previous good behavior and denial of major life events, are classic signs of **oppositional defiant disorder (ODD)**. - ODD involves a pattern of angry/irritable mood, argumentative/defiant behavior, or vindictiveness lasting at least 6 months, clearly distinguishing it from a temporary behavioral issue. *Attention deficit hyperactivity disorder* - While **ADHD** can cause inattention and difficulty following instructions, it typically presents earlier in childhood and is characterized by **hyperactivity**, **impulsivity**, and **inattention** that would have likely been prominent before recently. - The patient's primary symptoms here are an argumentative and defiant attitude rather than core symptoms of inattention or hyperactivity that began recently. *Antisocial personality disorder* - This disorder is typically diagnosed in **adulthood (18 years or older)**, although symptoms of **conduct disorder** must be present before age 15. The patient is currently 15. - **Antisocial personality disorder** involves a pervasive pattern of disregard for and violation of the rights of others, which is more severe than the defiance seen in this case. *Conduct disorder* - **Conduct disorder** involves a more severe pattern of behavior, including aggression towards people or animals, destruction of property, deceitfulness or theft, and serious violations of rules, which is not described in this patient. - The behaviors in this patient (argumentativeness, defiance) are less severe than the behaviors associated with conduct disorder. *Major depressive disorder* - Although behavioral changes can occur in **depression**, this patient does not exhibit other common symptoms such as **anhedonia**, changes in sleep or appetite, or persistent sadness, which would be expected with **major depressive disorder**. - His behaviors are primarily externalizing and defiant rather than indicating an internal state of sadness or loss of interest.

Clinical Reasoning Flashcard 1 of 10

Question: In Legg-Calve-Perthes, will you often observe pathology on the initial x-ray?_____

Answer: No

Clinical Reasoning Flashcard 2 of 10

Question: The diagnosis for diabetes mellitus may be made using _____ which reflects average blood glucose over 3 prior months

Answer: HbA1c

Clinical Reasoning Flashcard 3 of 10

Question: On a non-contrast head CT, acute bleeding appears as _____ lesions

Answer: hyperattenuated (bright)

Clinical Reasoning Flashcard 4 of 10

Question: What mnemonic is used to help in the diagnosis of measles (rubeola)?_____

Answer: 4 C's (cough, coryza, conjunctivitis, koplik spots)

Clinical Reasoning Flashcard 5 of 10

Question: tuberous sclerosis

Answer:

Extra Information: cutaneous angiofibromas (adenoma sebaceum), hypopigmented "ash leaf" spots, seizures, mental retardation, cortical and retinal hamartomas, renal cysts and angiomyolipomas, cardiac rhabdomyomas, astrocytomas AD, but incomplete penetrance and variable expressivityTSC1/TSC2

Clinical Reasoning Flashcard 6 of 10

Question: What is the most common clinical application for an ELISA?

Answer: detection of antibodies in patient blood sample

Clinical Reasoning Flashcard 7 of 10

Question: accuracy (diagnostic testing)

Answer: the "trueness" of a test's results

Clinical Reasoning Flashcard 8 of 10

Question: precision (diagnostic testing)

Answer: consistency and reproducibility of a test's results

Clinical Reasoning Flashcard 9 of 10

Question: What is the next step in diagnosis for a patient with new-onset epigastric pain, nausea, hypotension, bradycardia and T-wave inversions in leads II, III, aVF? _____

Answer: Right-sided precordial ECG

Extra Information:  Watch Stable Angina, Vasospastic Angina, & Acute Coronary Syndromes (UA, NSTEMI, STEMI) [https://dashboard.sketchy.com/study/medical/courses/medical-pathophysiology/units/medical-pathophysiology-cardiac/videos/medical-pathophysiology-cardiac-ischemic-heart-disease-stable-angina-vasospastic-angina-and-acute-coronary-syndromes-ua-nstemi-stemi?utm_source=anki&utm_medium=partnership&utm_campaign=february_update&utm_content=medical] https://onlinemeded.org/spa/cardiac?ref=anki 

Clinical Reasoning Flashcard 10 of 10

Question: Patients with psoas abscesses frequently position themselves to minimize psoas stretching and discomfort by engaging hip _____ and positioning into lumbar lordosis

Answer: flexion

Extra Information:  https://onlinemeded.org?ref=anki