Question 171#

A 55-year-old man with a history of type 2 diabetes mellitus, bipolar disorder and chronic obstructive pulmonary disease has bloods taken as part of his annual diabetic review: 

• Na⁺ 129 mmol/l
• K⁺ 3.8 mmol/l
• Bicarbonate 24 mmol/l
• Urea 3.7 mmol/l
• Creatinine 92 μmol/l

Due to his smoking history a chest x-ray is ordered which is reported as normal.

Which one of the following medications is most likely to be responsible?

A. Metformin

Correct Answer C: SIADH - drug causes: carbamazepine, sulfonylureas, SSRIs, tricyclics.

Lithium can cause diabetes insipidus but this is generally associated with a high sodium. Lithium only tends to cause raised antidiuretic hormone levels following a severe overdosage. Please see the BNF for more details. 

SIADH: causes:

Malignancy:

• Specially small cell lung cancer
• Also: pancreas, prostate

Neurological:

• Stroke
• Subarachnoid haemorrhage
• Subdural haemorrhage
• Meningitis/encephalitis/abscess

Infections:

• Tuberculosis
• Pneumonia

Drugs:

• Sulfonylureas
• SSRIs, tricyclics
• Carbamazepine
• Vincristine
• Cyclophosphamide 

Other causes: 

• Positive end-expiratory pressure (PEEP)
• Porphyrias

Question 172#

A cohort study is designed to look at the association between working long hours and blood pressure.

The following results are obtained after 10 years of follow-up:

What is the odds ratio of developing hypertension if you work more than 40 hours/week compared to people who work less than 40 hours/week? 

A. 60/600

Correct Answer C: 

• The odds of developing hypertension if you work < 40 hours/week is 50 / 1000 = 1 / 20 or 0.05
• The odds of developing hypertension if you work > 40 hours/week is 60 / 600 = 1 / 10 or 0.1
• The odds ratio is therefore = (odds of developing hypertension if you work > 40 hours/week) / (odds of developing hypertension if you work < 40 hours/week) = 0.1/0.05 = 2 

Odds and odds ratio:

Odds are a ratio of the number of people who incur a particular outcome to the number of people who do not incur the outcome. The odds ratio may be defined as the ratio of the odds of a particular outcome with experimental treatment and that of control.

Odds ratios are the usual reported measure in case-control studies. It approximates to relative risk if the outcome of interest is rare.

For example, if we look at a trial comparing the use of paracetamol for dysmenorrhoea compared to placebo we may get the following results:

• The odds of achieving significant pain relief with paracetamol = 40 / 20 = 2
• The odds of achieving significant pain relief with placebo = 30 / 60 = 0.5
• Therefore the odds ratio = 2 / 0.5 = 4

Question 173#

Which one of the following statements is true regarding the radial nerve?

A. Damage at the axilla would lead to wrist drop

Correct Answer A: 

Radial nerve:
Overview:

• Arises from the posterior cord of the brachial plexus (C5-8)

Motor to:

• Extensor muscles (forearm, wrist, fingers, thumb)

Sensory to: 

• Dorsal aspect of lateral 3 1/2 fingers
• However, only small area between the dorsal aspect of the 1st and 2nd metacarpals is unique to the radial nerve

Patterns of damage:

• Wrist drop
• Sensory loss to small area between the dorsal aspect of the 1st and 2nd metacarpals 

Axillary damage:

• As above
• Paralysis of triceps

Question 174#

The Framingham Heart Study is an example of a:

A. Cross-sectional survey

Correct Answer B: 

Study design:
The following table highlights the main features of the main types of study:

Question 175#

Osteogenesis imperfecta is due to a defect in which one of the following proteins?

A. Fibrillin

Correct Answer C: 

Osteogenesis imperfecta:
Osteogenesis imperfecta (more commonly known as brittle bone disease) is a group of disorders of collagen metabolism resulting in bone fragility and fractures. The most common, and milder, form of osteogenesis imperfecta is type 1

Overview:

• Autosomal dominant
• Abnormality in type 1 collagen due to decreased synthesis of pro-alpha 1 or pro-alpha 2 collagen polypeptides

Features:

• Presents in childhood
• Fractures
• Blue sclera
• Deafness secondary to otosclerosis