Question 111#

Which one of the following types of thyroid cancer is associated with the RET oncogene?

A. Anaplastic

Correct Answer D: The RET oncogene encodes a receptor tyrosine kinase and is associated with MEN type 2. Papillary thyroid cancer also appears to be associated with the RET oncogene.

Multiple endocrine neoplasia:

The table below summarises the three main types of multiple endocrine neoplasia (MEN):

MEN is inherited as an autosomal dominant disorder.

Question 112#

Which of the following statements is true regarding the p53 gene? 

A. It is an oncogene

Correct Answer D: p53 is a tumour suppressor gene located on chromosome 17p. It is the most commonly mutated gene in breast, colon and lung cancer p53 is thought to play a crucial role in the cell cycle, preventing entry into the S phase until DNA has been checked and repaired. It may also be a key regulator of apoptosis.

Li-Fraumeni syndrome is a rare autosomal dominant disorder characterized by the early onset of a variety of cancers such as sarcomas and breast cancer. It is caused by mutation in the p53 gene.

Question 113#

A 38-year-old woman comes for review. Six months ago she fractured her left wrist whilst skiing. The fracture was treated using a cast and repeat x-rays showed that the bone had healed well. Unfortunately for the past few weeks she has been plagued with ongoing 'shooting pains' in her left hand associated with swelling. On examination the left hand is extremely tender to even light touch. Her left hand is also slightly swollen compared to the right.

What is the most likely diagnosis?

A. Depression

Correct Answer C: 

Complex regional pain syndrome:
Complex regional pain syndrome (CRPS) is the modern, umbrella term for a number of conditions such as reflex sympathetic dystrophy and causalgia. It describes a number of neurological and related symptoms which typically occur following surgery or a minor injury. CRPS is 3 times more common in women.

There are two types of CRPS:

• Type I (most common): there is no demonstrable lesion to a major nerve
• Type II: there is a lesion to a major nerve

Features:

• Progressive, disproportionate symptoms to the original injury/surgery
• Allodynia
• Temperature and skin colour changes
• Oedema and sweating
• Motor dysfunction
• The Budapest Diagnostic Criteria are commonly used in the UK

Management:

• Early physiotherapy is important
• Neuropathic analgesia in-line with NICE guidelines
• Specialist management (e.g. Pain team) is required

Question 114#

A new blood test to screen patients for heart failure is trialled on 500 patients. The test was positive in 40 of the 50 patients shown to have heart failure by echocardiography. It was also positive in 20 patients who were shown not to have heart failure.

What is the positive predictive value of the test?

A. 0.8

Correct Answer B: A contingency table can be constructed from the above data, as shown below:

Positive predictive value = TP / (TP + FP) = 40 / (40 + 20) = 0.66

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.

Question 115#

What are funnel plots primarily used for?

A. Demonstrate the heterogeneity of a meta-analysis

Correct Answer B: Funnel plots - show publication bias in meta-analyses.

Funnel plot:
A funnel plot is primarily used to demonstrate the existence of publication bias in meta-analyses. Funnel plots are usually drawn with treatment effects on the horizontal axis and study size on the vertical axis.

Interpretation:

• A symmetrical, inverted funnel shape indicates that publication bias is unlikely
• Conversely, an asymmetrical funnel indicates a relationship between treatment effect and study size. This indicates either publication bias or a systematic difference between smaller and larger studies ('small study effects')