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Diagnosing appendicitis and cholecystitis by numbers

Dr Nick Summerton shows how numerical data derived from the history and examination can help in diagnosing two common surgical conditions

Dr Nick Summerton shows how numerical data derived from the history and examination can help in diagnosing two common surgical conditions

Data on the diagnoses in more than 10,000 patients with acute abdominal pain reveal that inflammation of the appendix and gall bladder represent the majority of acute abdominal problems referred to surgical departments.

It is always very satisfying to get the diagnosis of appendicitis correct but it can be quite tricky and textbooks are full of advice which is sometimes contradictory.

41196191The majority of patients encountered in primary care settings with upper abdominal pain are subsequently found to have a relatively benign cause for the pain but acute cholecystitis still warrants consideration. The two boxes below show the relevant likelihood ratios.

Definitions

Likelihood ratios

The likelihood ratio is the ratio of the probability of an event (such as a symptom) in diseased persons to the probability of that same event in non-diseased persons.

Likelihood ratios indicate how many times more (or less) likely a result is in a patient with the disease compared with a patient free of the disease.

The adjectives ‘positive' or ‘negative' indicate whether the likelihood ratio refers to the presence of the clinical information (positive) or the absence of the information (negative).

Positive likelihood ratios with the highest value argue most for the disease when the clinical information is present.

Negative likelihood ratios with the value closest to zero argue the most against the disease when that information is absent.

Reliability (or reproducibility) is the extent to which repeated measurements of a stable phenomenon produce similar results.

Kappa statistic is the term for how this level of agreement of measurements is expressed, as a chance-corrected proportional value.

Kappa values greater than 0.80 may be taken to represent almost perfect agreement, values between 0.61 and 0.80 substantial agreement, values between 0.41 and 0.60 moderate agreement, values between 0.21 and 0.40 slight agreement and values of 0.20 or below represent poor agreement beyond chance.

Discussion

It is important to appreciate that some of the signs of appendicitis (such as rigidity, guarding, rebound tenderness and cough tenderness) are also general signs of peritoneal irritation.

However, finding a patient with pain and tenderness in the right iliac fossa, especially if they have McBurney's point tenderness, a positive cough test and a positive Rovsing's sign, argues strongly in favour of appendicitis.

One caveat is that some of the signs listed above that appear to have reasonable likelihood ratios exhibit poor inter-observer reliability.

The kappa value for guarding is 0.36 (slight agreement), for rebound tenderness 0.25 (slight agreement) and for rigidity is only 0.14 (poor agreement).

Murphy's sign refers to pain and arrested inspiration occurring when an examiner's fingers are hooked underneath the right costal margin during deep inspiration.

A positive Murphy's sign together with the presence of right upper quadrant tenderness and pain, fever and vomiting suggests cholecystitis.

The presence of back tenderness argues against the diagnosis possibly because it is found more commonly in alternative diagnoses such as renal disease or pancreatitis.

Dr Nick Summerton is a GP in Yorkshire and clinical lead for BMI Healthcare

This article is based on Patient-Centred Diagnosis, by Dr Nick Summerton published by Radcliffe Publishing, ISBN 9781846190551. Pulse readers can claim a 15% discount when they buy direct from Radcliffe by telephoning 01235 528820 or online at www.radcliffe-oxford.com by putting PULSEPCD in the discount code box at the checkout

Likelihood ratios Key messages

• Inflammation of the appendix and gall bladder represent the majority of acute abdominal problems referred to surgical departments.
• Pain and tenderness in the right iliac fossa (LR+ 7.3), especially if there is McBurney's point tenderness (LR+ 3.4), a positive cough test (LR+ 2.4), and a positive Rovsing's sign (LR+ 2.5), argue strongly in favour of appendicitis.
• A positive Murphy's sign (LR+ 2.8) together with the presence of right upper quadrant tenderness and pain (LR+ 1.5/1.6), fever (LR+ 1.5) and vomiting (LR+ 1.5) suggest cholecystitis. The presence of back tenderness (LR- 2.0) argues against the diagnosis.
• Some traditional clinical findings are unreliable: the kappa value for guarding is 0.36 (slight agreement), for rebound tenderness 0.25 (slight agreement) and for rigidity is only 0.14 (poor agreement).

Right upper quadrant pain or tenderness could be indicative of cholecystitis Abdominal exam

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