INTRODUCTION
Chronic pain: a symptom or
a disease?
This short overview addresses key concepts to align the definitions and concepts of chronic pain
Bart Morlion MD PhD
The Leuven Center for
Algology, University
Hospitals, Leuven,
KU Leuven, Belgium
Pain is one of the most common reasons for
a patient to consult a healthcare professional.
One in five adults in Europe is estimated to be
affected by chronic pain. 1
What is pain?
A frequently used definition of pain was proposed by
the International Association for the Study of Pain
(IASP): “Pain is an unpleasant sensory and emotional
experience associated with actual or potential tissue
damage or described in terms of such damage”. 2 Our
nociceptive system is one the fastest and most
sensitive defense mechanisms in our body. Mostly,
acute pain can be considered as a symptom of an
underlying activation of our warning system by
internal and/or external harmful stimuli.
Recently, the definition of pain has been
challenged by alternative proposals. The IASP
Definition of Pain Taskforce suggests to define pain
as “An aversive sensory and emotional experience
typically caused by, or resembling that caused by,
actual or potential tissue injury”. 3 Another proposal
from 2016 suggests: “Pain is a distressing experience
associated with actual or potential tissue damage,
with sensory, emotional, cognitive and social
components.” 4 Importantly, all these definitions
imply the subjective nature of pain experiences.
What are pain descriptors?
Aside from the distinction between acute and
chronic pain, pain syndromes can be divided into
three classes according to their clinical features
and aetiology.
Class 1: Nociceptive pain
Nociceptive pain, is physiological protective pain
involving activation of high-threshold nociceptor
neurons by noxious mechanical, chemical or
thermal stimuli (for example, ligamentous stretch
or pinprick).
Class 2: Inflammatory pain
Inflammatory pain is pain hypersensitivity involving
detection of active peripheral tissue inflammation
by nociceptors and sensitisation of the nociceptive
system (for example, facet pain or spondylodiscitis).
Class 3: Pathological pain
The third class, pathological pain, is not a symptom
but, rather, represents a disease state of the nervous
system. Pathological pain is not adaptive and has no
protective function, and can be divided into two
types: nociplastic and neuropathic. Nociplastic pain
is the result of nociceptive signaling amplification in
the absence of neural lesions or inflammation (for
example, fibromyalgia or chronic widespread pain). 5
Conversely, neuropathic pain is a maladaptive
plasticity that may or may not be due to a lesion or
disease, and affects the somatosensory system and
alters nociceptive signal processing so that
responses to noxious and innocuous stimuli are
enhanced and pain is felt in the absence of stimuli
(for example, radicular pain).
What is chronic pain?
A classification according to duration, speed and
time will categorise pain either as acute or chronic.
Acute and chronic pain are totally different types of
pain. Chronic pain is not just an extension of acute
pain. Yet, the duration of the pain is the first
criterion to distinguish acute and chronic pain. For
many years, chronic pain was defined as “pain
without apparent biological value that has persisted
beyond the normal tissue healing time (usually
about three months)”. 6,7
Recently, the International Classification of
Diseases defined chronic pain as pain that lasts
or recurs for longer than three months. 8
Although chronic pain may be a symptom of an
underlying chronic condition, it frequently outlasts
the normal healing process and often no other
underlying disease can be identified. The common
understanding is that, unlike acute pain, chronic
pain has no protective function.
Over the last decades, the paradigm of chronic
pain shifted from a pure biomedical to
a biopsychosocial phenomenon. Indeed, the
biopsychosocial model of chronic pain recognises
chronic pain as a combination of physical
dysfunction, beliefs, coping strategies, distress,
illness behaviour and social interactions. Since the
introduction of the biopsychosocial model,
treatment of chronic pain has become multimodal
and multidisciplinary, with the aim of maximising
pain reduction, quality of life, independence and
mobility.
What is pain chronification?
The transition from acute to chronic pain is a very
complex process involving a plethora of
neurobiological and psycho-neurophysiological
processes. The development and maintenance of
many chronic pain syndromes appears to arise from
an imbalance between amplified ascending signals
and inadequate activation of the descending
inhibitory pathways. A common process is central
sensitisation which is defined as “increased
responsiveness of nociceptive neurons in the central
nervous system to their normal or subthreshold
afferent input”. 9
hospitalpharmacyeurope.com | 2019 | 3