The spinal facet joints, intervertebral discs, muscles and ligaments are all potential sources of mechanical back pain, a pain derived from the damaged or injured tissues and transmitted by the nervous system. When the nervous system is damaged or injured it can start generating pain itself, leading to the production of what is termed neuropathic pain. Typical diagnoses of this kind of pain are post-shingles pain, phantom pain, nerve root damage pain and diabetic neuropathy pain. Patients suffer badly with this kind of unpleasant pain and it is difficult to treat.

Researchers from Addenbrooke’s Hospital in Cambridge UK and Massachusetts General Hospital in Boston have investigated the diagnostic difficulty stated above. The pain processes which are occurring in many cases are very complex and this is not reflected in the assessment process of merely investigating the area of pain and its intensity. They attempted to design a tool for assessment which would recognise the complexities, narrow the options for a diagnostic decision and perhaps lead to more appropriate management. A standardised tool was developed to assess chronic back pain so that the underlying pain subtypes could be identified.

The researchers tested fifty-seven patients with typical low back pain and one hundred and thirty with peripheral neuropathic pain were investigated in a repeatable manner by a standardised group of sixteen questions then a physical examination consisting of 23 particular tests. Pain descriptors in terms of a series of words to describe pain were presented to patients who then chose the ones most applicable to their pain. Alteration in the ability to accurately sense pin-prick, light touch and vibration inputs is altered in chronic pain syndromes and the ability to accurately distinguish these modalities is also assessed.

Identification was possible of six subgroups of neuropathic pain patients and two subgroups of patients with non-neuropathic pain. The researchers were also able to identify the six questions and ten physical tests which did the best job of making the discrimination between these various types of pain. They then tested the revised diagnosis tool on another group of 137 patients and reported it worked well and patients found it acceptable. They found that a small number of symptoms and signs can distinguish a distinct set of subtypes of neuropathic pain but that these types were not determined by the underlying condition which caused the pain.

Neuropathic pain patients are usually categorised by the disease which is causing their pain but the researchers found that there was no connection between the types of neuropathic pains exhibited and the underlying diseases the patients suffered from. In one disease there may be different pain mechanisms generating pain and in several different diseases the same mechanism of pain production may be active. There may also be a variation in the types of pain production within one individual. The differential diagnosis between mechanical spinal pain and nerve root pain was distinguished by the test, a sometimes difficult task as there can be small changes in the muscle power and skin sensibility.

Patients with neuropathic pain are generally diagnosed as to the causal disease they exhibit, but the researchers did not find a connection between the diseases patients had and the types of neuropathic pain they showed. Several underlying mechanisms of pain production may occur in patients with the same disease and the same pain production can occur in patients across several diagnoses. The types of pain mechanism producing pain in individuals may also vary over time. The tests help to distinguish between nerve root involvement and segmental spinal pain. This can be difficult as nerve root pain can present with minor sensory or motor changes and segmental pain can refer to the limbs.