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Diagnosis by numbers - could that headache be temporal arteritis?

In this first article, Dr Nick Summerton shows how numerical data derived from the history and examination can, with test results, help in making a difficult diagnosis

In this first article, Dr Nick Summerton shows how numerical data derived from the history and examination can, with test results, help in making a difficult diagnosis

Introduction

Temporal arteritis is a particular concern for GPs when dealing with older patients presenting with headaches. Although the prevalence is estimated to be only 0.15% for patients over 50, timely diagnosis and treatment with high-dose steroids can prevent visual loss.

Most of us are well aware that the ESR has a place in the diagnosis – but insufficient emphasis is given to the value of information obtained directly from the patient via the history or the clinical examination.

41195665There is a range of reported symptoms and signs for temporal arteritis and the positive and negative likelihood ratios for some of these are detailed in the attached table (for link, see right).

Likelihood ratio is an important term here. Likelihood ratios indicate how many times more (or less) commonly a result or symptom is seen in a patient who has the disease than it is in a patient who does not have it.

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

Positive likelihood ratios with the highest value argue most for disease when the clinical information is present; negative likelihood ratios with the value closest to zero argue the most against disease when that clinical information is absent.

Discussion

The headache of temporal arteritis is often non-specific in character and it seems that a temporal location only confers a positive likelihood ratio of 1.5 and a tender scalp only 1.6.

However, pain in the proximal jaw near the temporomandibular joint that develops after a brief period of chewing (especially for food requiring a lot of mastication such as tough meat) – jaw claudication – provides a positive likelihood ratio of 4.2.

The presence of diplopia also substantially increases the likelihood of disease (LR + 3.4). But it is important to note that the negative likelihood ratios of these two features are only 0.7 and 0.9 respectively, indicating that their absence is much less helpful in arguing against the diagnosis of temporal arteritis.

41195663It is particularly interesting to compare the magnitude of the likelihood ratios obtained from the medical history and the clinical examination with those provided by various levels of ESR results (see left).

The key point is that the information obtained from the patient should be considered as carefully as any ESR result in assessing an older person with a headache.

Dr Nick Summerton is a GP in Yorkshire and clinical lead at 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 Radcliffe-Oxford by putting PULSEPCD in the discount code box at the checkout.

Temporal arteritis Likelihood ratios for temporal arteritis Range of ESR Key messages Patient-centred diagnosis

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