AIPGMEE 2015

1. 1. Epidemiology is broadly defined as the study of factors that influence the health of populations. The application of epidemiologic findings to decisions in the care of individual patients is:
   A.    Generally inappropriate
   B.     Known as clinical epidemiology
   C.     Limited to chronic disease epidemiology
   D.    Limited to infectious disease epidemiology
   E.     Limited to biologic mechanisms rather than social and environmental considerations
   Answer
   B. Clinical practice is devoted to the care of individual patients. Outcomes in individual patients in response to clinical interventions cannot be known, however, until after the interventions have been tried. The basis for choosing therapy (or for choosing diagnostic tests) is prior experience in similar patients, rather than knowledge of what would work best for the individual. The use of clinically applied statistics, probability, and population-based data to inform medical decisions is known as clinical epidemiology. Clinical epidemiology pertains to all clinical care. Its findings and applications are not limited to infectious diseases (D) or chronic diseases (C), or to biologic mechanisms (E). Social and environmental considerations are very relevant to clinical decision making (E). Far from being inappropriate (A), the application of epidemiologic principles to patient care is fundamental to evidence-based practice and is supportive of robust clinical decisions.
   2.      Tim has a severe heart attack at age 58. The near-death experience so scares Tim that he quits smoking. Tim’s wife is also scared into quitting smoking even though she feels fine. Tim’s son resolves never to start smoking, seeing what cigarettes have done to his dad. The act of not smoking for Tim, Tim’s wife, and Tim’s son represents:
   A.    Host, vector, and agent effects, respectively
   B.     Herd immunity
   C.     Tertiary prevention for Tim’s son
   D.    Tertiary prevention, primary prevention, and secondary prevention, respectively
   E.     Tertiary prevention, secondary prevention, and primary prevention, respectively
   Answer
   E. Prevention means intervening to interrupt the natural history of disease. Primary prevention represents the earliest possible interventions to foil disease before it even begins (e.g., Tim’s son never starting to smoke). Secondary prevention is thwarting the progression of established disease that has not yet declared itself with symptoms or outward signs (e.g., Tim’s asymptomatic wife quitting smoking). Tertiary prevention is slowing, arresting, or even reversing obvious or symptomatic disease to prevent worsening symptoms and further deterioration (e.g., Tim quitting smoking after his heart attack). Answer choices (C) and (D) get distinctions between these stages of disease prevention wrong. Herd immunity (B) is the prevention of disease transmission to susceptible individuals through acquired immunity in others. Herd immunity does not apply to the scenario involving Tim and his family. Likewise, definitions for host (i.e., susceptible individual), vector (i.e., unaffected carrier), and agent (i.e., medium of harm) (A) do not apply to the characterizations of Tim and his family.
   
   

AIPGMEE 2015

A 73-year-old man collapses at home following a stroke. He is found 24 hours later, still lying on the floor. On admission to hospital he appears only mildly dehydrated but is in acute renal failure. He is treated with i.v. fluids but remains oliguric and his renal function continues to deteriorate. Dipstick urinalysis is strongly positive for blood but microscopy reveals no red cells. What is the most likely diagnosis?

• Renal calculus
• Urinary sepsis
• Rapidly progressive glomerulonephritis
• Renal infarction
• Rhabdomyolysis

All of the options listed could conceivably account for deteriorating renal function accompanied by dipstick-positive haematuria, but the absence of red cells on microscopy is characteristic of myoglobinuria occurring as a consequence of rapid muscle breakdown. This patient is at risk of rhabdomyolysis from having lain on the floor for 24 hours.

More on Interpretation of dipstick-positive haematuria (p. 479)

AIPGMEE 2015

A 73-year-old man presents with a right hemiparesis and expressive dysphasia secondary to an infarct in the territory of the left middle cerebral artery. Blood pressure is 153/82 mmHg, serum cholesterol is 4.4 mmol/L and the ECG shows sinus rhythm with no abnormalities. Which of the following medications is least likely to be of benefit in preventing a further ischaemic stroke?

• Ramipril
• Bendroflumethiazide
• Aspirin
• Warfarin
• Simvastatin

In addition to lifestyle modifications, antiplatelet, lipid-lowering and antihypertensive therapy forms the cornerstone of secondary prevention for most patients with an ischaemic stroke. Recent large-scale randomised trials have demonstrated the benefit of statins and antihypertensives in these patients, even with blood pressure and cholesterol levels within the ‘normal’ range. Patients in atrial fibrillation benefit from anticoagulation with warfarin following ischaemic stroke, but there is no such benefit in those who are in sinus rhythm. The evidence base for stroke secondary prevention is included in the book, as below.

More on Secondary prevention of stroke (p. 1188)

AIPGMEE 2015

The best radiologic modality to diagnose gallbladder stones is:

• Computed tomography (CT)
• Ultrasonography
• HIDA scan (technetium 99–labeled iminodiacetic acid)
• Percutaneous transhepatic cholangiography (PTC)
• Kidney-ureter-bladder (KUB) radiograph

Ultrasound is quick, non-invasive and has a 88% sensitiviy for the detection of galltones. It is generally the first modality used to evaluate cholelithiasis. HIDA scans are helpful for determining acute cholecystitis. PTC is used to visualize the intrahepatic and extrahepatic biliary tree. CT is useful in the evaluation of the acute abdomen, providing excellent visualization of the pancreas, mesentery, liver, retroperitoneum, and gallbladder. Although CT will allow excellent visualization of the gallbladder wall, its sensitivity for the detection of gallstones is poor. However, its detection of renal stones is more accurate than renal ultrasonography.

AIPGMEE 2015

The superior mesenteric artery is derived from which of the following?

• Posterolateral arteries
• Lateral arteries
• Ventral arteries

The superior mesenteric artery is derived from ventral branches of the dorsal aorta, specifically the vitelline arteries.

Argyll Robertson pupils and light–near dissociation

Argyll Robertson pupils and light–near dissociation

DESCRIPTION

Arygll Robertson pupils are characterised by:

1.                  small pupils

2.                  absence of the pupillary light response

3.                  brisk accommodation reaction

4.                  bilateral involvement.

Light–near dissociation is defined as:

1.                  a normal accommodation response

2.                  a sluggish or absent pupillary light response.

Light–near dissociation is said to be present if the near pupillary response (tested in moderate light) exceeds the best pupillary response with a bright light source.⁹ Light–near dissociation is associated with Argyll Robertson pupils (classically, a sign of tertiary syphilis).

RELEVANT NEUROANATOMY AND TOPOGRAPHICAL ANATOMY

Accommodation and pupillary light pathways

AFFERENT STRUCTURES

·                            Retinal neuroepithelium

↓

·                            Optic nerve (CNII)

↓

·                            Pretectal nucleus midbrain

↓

·       Bilateral innervation of Edinger–Westphal nuclei

↓

EFFERENT STRUCTURES

·                            Visual cortex (accommodation only)

↓

·                            Accommodation area, visual cortex (accommodation only)

↓

·                            Pretectal nuclei, midbrain

↓

·                            Edinger–Westphal nuclei, midbrain

↓

·                            Oculomotor nerve (CNIII)

↓

·                            Ciliary ganglion

↓

·                            Short ciliary nerves

↓

·       Pupillary constrictor muscles

·       Ciliary muscle

·       Medial rectus muscles

CONDITION/S ASSOCIATED WITH

·                     Multiple sclerosis

·                     Neurosarcoidosis

·                     Tertiary syphilis

MECHANISM/S

Argyll Roberston pupils and light–near dissociation are caused by a pretectal lesion in the dorsal midbrain affecting the fibres of light reflex, which spare the fibres of the accommodation pathway that innervate the Edinger–Westphal nuclei

SIGN VALUE

Argyll Robertson pupils are classically a sign of tertiary syphilis. Tertiary syphilis is no longer the most common cause of light–near dissociation.

AIPGMEE 2015

A 14-day-old baby is admitted to the hospital with a fever, hyperactivity, and a stiff neck. At the time of giving birth to the baby, the mother complained of flulike symptoms. Blood and CSF were collected for culture. No organisms were seen in the Gram stain of the CSF; however, the culture of blood and CSF became positive after 48 hours of incubation. Colonies appeared weakly beta-hemolytic, and the Gram stain was interpreted as gram-positive cocci or coccobacilli arranged in single cells and pairs. Which organism is most likely responsible for this baby’s infection?

• Escherichia coli
• Listeria monocytogenes
• Neisseria meningitidis
• Group B Streptococcus agalactiae
• Streptococcus pneumonia

Although L. monocytogenes is most likely the bacterium that caused the meningitis, it is important to note first that all five of the bacteria listed in this question can also cause the disease. E. coli and group B S. agalactiae are primarily restricted to babies less than 1 month of age, whereas L. monocytogenes, N. meningitidis, and S. pneumoniae can cause meningitis in all age groups. (N. meningitidis is most common in young adults, whereas the other two bacteria cause disease most commonly in the young and the very old.) The baby’s meningitis is most likely caused by L. monocytogenes because the organism is a slow-growing, weakly beta-hemolytic, gram-positive coccobacillus. In contrast with other organisms, L. monocytogenesgrows slowly in CSF and typically is not observed in a Gram stain of CSF because relatively few organisms are present. When observed by Gram stain, L. monocytogenes may be mistaken forS. pneumoniae. Organisms isolated in culture are readily differentiated by colonial morphology (S. pneumoniae is alpha-hemolytic) and simple phenotypic tests. E. coli and N. meningitidisare gram-negative and should not be mistaken for L. monocytogenes. S. agalactiae is a gram-positive cocci but grows well on blood agar and appears as long chains rather than single cells or pairs.