Patients in pain

Introduction

Pain is a familiar phenomenon that is part of our everyday life and is a feature of various diseases. It most commonly accompanies an injury, where it serves its most important purpose, namely, to protect us, alert us and make us remove ourselves from danger. It can possibly trigger a spinal withdrawal reflex ( Fig. 11.1 ). Both congenital insensitivity to pain and extreme sensitivity to pain (paroxysmal extreme pain disorder and erythromelalgia) are rare genetic conditions, which are disabling and shorten life span, highlighting the importance of pain to our welfare and survival. Pain severity and its impact on an individual ranges from a trivial occurrence, such as a needle-prick injury, to a sensation of such intensity that it induces thoughts of suicide.

Definition

The International Association for the Study of Pain (IASP) proposed the following definition (1979): ‘Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of damage’. This definition has important implications. Pain is not necessarily or always associated with ongoing tissue damage; rather, it is a subjective experience and has an emotional as well as a sensory component and is always unpleasant.

Pain is notoriously difficult to describe and even harder to assess and quantify. Nevertheless, pain assessment is crucial in order to evaluate its impact on the sufferer and also to plan a treatment strategy. It has been termed ‘the 5th vital sign’ and is mandated as part of routine assessment of patients in hospital. In 2004 the IASP declared that the relief of pain should be a human right.

Although pain is a major source of suffering and economic burden for patients, until recently, it was not considered as a separate condition and systematically classified. Recognizing this, the World Health Organisation (WHO), in their recent adoption of the International Classification of Diseases (ICD-11) in May 2019, for the first time included chronic or long-standing pain as an independent disease and paved the way for a systematic classification of the condition.

Classification of pain

There are many ways in which pain can be classified in order to formulate an optimal treatment strategy. Despite this, classifying a particular pain state can be challenging because the pain syndrome may be of mixed aetiology rather than fit into a single category.

Pain is commonly classified according to the following:

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  Aetiology and underlying condition

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  Mechanism

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  Duration