What is a diagnosis?
While there is no uniform definition of diagnosis, different definitions converge to the following: the process of designating a pathological condition using symptoms, signs, and tests. Does it apply to chronic pain?
What are the purposes of making a diagnosis?
A diagnosis provides an explanatory framework to identify potential causes of a disease. For example, shingles (herpes zoster) can cause chronic pain. Therefore, the diagnosis of "post-herpetic neuralgia" identifies the trigger (the shingle infection) of a disease (neuropathic pain in medical language or "nerve" pain in lay language).
A diagnosis may allow the identification of treatments that potentially work for a disease. For instance, the diagnosis of migraine is based on a group of symptoms and signs as determined by the International Headache Society, and patients who are diagnosed according to these criteria can respond to migraine-specific treatments.
Finally, diagnoses allow the classification of diseases. In the field of pain, the International Association for the Study of Pain (IASP) has provided a diagnosis-based classification (see here).
"Diagnosis" is an heterogeneous construct
Some examples:
Post-herpetic neuralgia: As mentioned above, this diagnosis implies a cause (herpes infection) and the anatomical source (nervous system) of the pain.
Facet joint pain: This diagnosis implies only the source of pain (the facet joints that connect adjacent segments of the spine), but not the cause.
Fibromyalgia: A combination of symptoms and signs, based on expert consensus, without implying any cause, mechanism, or source of pain.
Low back pain: This designates the location (low back) of a symptom (pain).
Having a diagnosis does not mean understanding the patient's problem
Let's consider the diagnosis of facet joint pain. The most widely accepted way to make this diagnosis is performing nerve blocks: if anesthetizing the nerves that supply the facet joints produce pain relief, we conclude that our patient is likely to have facet joint pain. However, this remains a pure anatomical diagnosis, and does not tell us why the facet joint is hurting. For instance, is the pain caused by arthritis? Even if arthritis is detected by imaging, there is a poor association (if any) between image finding of arthritis and pain, as arthritis can be present without any pain.
Is "pain" a diagnosis?
For instance, is low back pain a diagnosis, just a symptom, or both? Let's consider again the definition of diagnosis: the process of designating a pathological condition using symptoms, signs, and tests. Based on this definition, most health care professionals may question the legitimacy to consider "low back pain" a diagnosis. Pain is commonly regarded as a symptom that would lead to a diagnosis.
However, the International Association for the Study of Pain (IASP), and most of the scientific community, consider certain forms of pain a disease per se and not merely a symptom. For this reason, the IASP has introduced the term "chronic primary pain" in its a diagnosis-based classification, defined as: "pain in one or more anatomical regions that persists or recurs for longer than 3 months and is associated with significant emotional distress or functional disability (interference with activities of daily life and participation in social roles) and that cannot be better accounted for by another chronic pain condition" (see here).
The new IASP definition represents a paradigm-change in the way health care professionals should view pain. In the specific case, chronic low back pain is considered as health conditions in its own, rather than a symptom that lacks a diagnosis. Other chronic primary pain syndromes include, among others, fibromyalgia, chronic primary headache, certain forms of orofacial, and pain associated with irritable bowel syndrome.
A more comprehensive way to determine a diagnosis
Chronic pain is frequently associated with emotional and physical dysfunction. Therefore, the addition of elements of emotional and physical functioning would be an important enrichment in the diagnostic characterization of patients with chronic pain. There is an enormous difference between a patient with daily low back pain, who can sleep and is in a stable mental health, and a patient with the same "amount" of low back pain, who cannot sleep more than few hours, is severely depressed, and unable to walk more than few blocks. Having these two patients within the same category of chronic low back pain raises many questions on the usefulness of a such a diagnosis.
While we have done the essential step to recognize chronic pain as a disease per se, work remains to be done to translate the complexity and heterogeneity of this condition into meaningful diagnoses. While this process is still ongoing in the scientific community, health care professionals should consider the multidimensionality of pain when they make their diagnosis. Only this approach
will satisfy the main purposes of diagnosing a condition, namely to provide an explanatory framework for the individual patient's problem, and identify promising treatment strategies.