A study is performed comparing two chemotherapy regimes for patients with small cell lung cancer. The end point of the study is survival time.
Which one of the following types statistical measures is most appropriate to compare survival time?
Correct Answer D:
Hazard ratio:
The hazard ratio (HR) is similar to relative risk but is used when risk is not constant to time. It is typically used when analyzing survival over time.
You are caring for a local cardiology consultant's father who has been admitted following a myocardial infarction. He bleeps you from the switchboard and asks how his father is doing. You recognize his voice on the phone.
What is the most appropriate response?
Correct Answer C: The main nub of this question relates to confidentiality. You cannot give details over the phone to anyone, even his son, without the patient's express permission. Whilst it may be presumed that this is what the patient would want it is impossible to be sure of the family dynamics.
If the patient has given permission and you are sure you are speaking to the son then giving relevant details is the best option. Asking the consultant to come in as an option but may not be necessary if the previous conditions are met. Saying he is 'doing fine' is unlikely to satisfy a consultant cardiologist.
Giving details without first getting permission from the patient is breaking confidentiality, however well intentioned. Involving a relative in the management of a patient is inappropriate and the worst option.
A contingency table is constructed for a new blood protein marker to screen for prostate cancer in men aged between 50 and 70 years:
What is the positive predictive value of the new test?
Correct Answer C:
Positive predictive value = true positives / (true positives + false positives) = 19 / (19 + 20)
Screening test statistics:
It would be unusual for a medical exam not to feature a question based around screening test statistics. The available data should be used to construct a contingency table as below:
TP = true positive; FP = false positive; TN = true negative; FN = false negative
The table below lists the main statistical terms used in relation to screening tests:
Positive and negative predictive values are prevalence dependent. Likelihood ratios are not prevalence dependent.
A 45-year-old man who is known to have Marfan's syndrome presents with lower back pain. This has been present for a few months now and is associated with headaches, leg pain and intermittent episodes of urinary incontinence.
What is the most likely diagnosis?
Correct Answer E: Dural ectasia affects around 60% of patients with Marfan's syndrome. It may cause lower back pain associated with neurological problems such as bladder and bowel dysfunction.
Marfan's syndrome:
Marfan's syndrome is an autosomal dominant connective tissue disorder. It is caused by a defect in the fibrillin-1 gene on chromosome 15 and affects around 1 in 3,000 people.
Features:
The life expectancy of patients used to be around 40-50 years. With the advent of regular echocardiography monitoring and beta-blocker/ACE-inhibitor therapy this has improved significantly over recent years. Aortic dissection and other cardiovascular problems remain the leading cause of death however.
Pellagra is caused by a deficiency in:
Pellagra:
Pellagra is a caused by nicotinic acid (niacin) deficiency. The classical features are the 3 D's - dermatitis, diarrhoea and dementia.
Pellagra may occur as a consequence of isoniazid therapy (isoniazid inhibits the conversion of tryptophan to niacin) and it is more common in alcoholics.
Broad hyperpigmented ’collar-like’ scaly plaques on the photo-exposed area of the neck and upper chest in a patient with pellagra; often referred to as the Casal necklace.
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