A 60-year-old woman with a history of hypothyroidism and inflammatory arthritis is admitted after slipping on ice and falling over. Some routine blood tests are performed:
Which one of the following is most likely to explain these results?
Correct Answer A: Renal tubular acidosis causes a normal anion gap.
The low bicarbonate suggests an acidosis. The anion gap is however normal, (141 + 2.9) - (114 + 16) = 13.9 mmol/l. The different diagnosis is therefore causes of a metabolic acidosis with a normal anion gap.
Aspirin and diabetic ketoacidosis causes a metabolic acidosis associated with a raised anion gap. Conn's syndrome would explain the hypokalaemia but it does not cause a metabolic acidosis. Renal tubular acidosis type 4 is associated with hyperkalaemia. The correct answer is therefore renal tubular acidosis type 1, which is likely to be secondary to this patient's inflammatory arthritis.
Metabolic acidosis:
Metabolic acidosis is commonly classified according to the anion gap. This can be calculated by:
(Na+ + K+) - (Cl- + HCO3-).
If a question supplies the chloride level then this is often a clue that the anion gap should be calculated. The normal range = 10-18 mmol/L.
Normal anion gap ( = hyperchloraemic metabolic acidosis):
Raised anion gap:
Metabolic acidosis secondary to high lactate levels may be subdivided into two types:
A 12-year-old girl develops facial swelling and an erythematous itchy rash shortly after being administered the first dose of the HPV vaccine. On arrival the paramedics note a bilateral expiratory wheeze and blood pressure of 80/50 mmHg.
In the Gell and Coombs classification of hypersensitivity reactions this is an example of a:
Correct Answer A: Anaphylaxis = type I hypersensitivity reaction.
Hypersensitivity:
The Gell and Coombs classification divides hypersensitivity reactions into 4 types:
Type I - Anaphylactic:
Type II - Cell bound:
Type III - Immune complex:
Type IV - Delayed hypersensitivity:
Type V - Stimulated hypersensitivity:
A 64-year-old female with a history of rheumatoid arthritis presents with increased difficulty in walking. On examination there is weakness of ankle dorsiflexion and of the extensor hallucis longus associated with loss of sensation on the lateral aspect of the lower leg.
What is the most likely diagnosis?
Correct Answer C:
Common peroneal nerve lesion:
The sciatic nerve divides into the tibial and common peroneal nerves. Injury often occurs at the neck of the fibula.
The most characteristic feature of a common peroneal nerve lesion is foot drop.
Other features include:
A study looks at the use of bisphosphonates in controlling the pain associated with bone metastases. One hundred and twenty patients (120) are enrolled in the study, 40 of whom are given conventional treatment with NSAIDs and radiotherapy. Of the 80 patients who were given bisphosphonates, 40 received significant pain relief.
What is the odds of patient with bone metastases receiving significant pain relief from bisphosphonates?
Correct Answer D: The question is limited to the 80 patients who've been given bisphosphonates. 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. 40 of the 80 patients received significant pain relief.
It can therefore be inferred that 40 of the 80 patients did not receive significant pain relief. Therefore the odds are 40 / 40 = 1.
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:
As part of a research project you are trying to ascertain whether the use of dummies in infants is linked to sudden infant death syndrome.
What is the most appropriate form of study design?
Correct Answer D: As sudden infant death syndrome is relatively rare a case-control design is more appropriate than a cohort study.
Study design: The following table highlights the main features of the main types of study:
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