Pain

Chronic Pain and its Relation to Brain Injury
By Gabriel G. de la Torre
Neuropsychologist and founder

Though There are some references to the topic of pain and its implications in neuropsychological rehabilitation and neuropsychology issues (Monguio, 1999), these still are not many. Pain represents a important variable to keep in mind in neuropsychology, even more if we are talking about chronic pain. Many of the patients that suffer from Head Injury usually present multiple sequelae ranging from cognitive and behavioral to physical and many times pain. Pain may appear not only in the most acute head injury cases but in other mild head injuries, contusions and concussions. This is why some methods applied in neuropsychology should count with the presence of pain and its consequences in the execution and recovery levels of these patients besides the effects of this circumstance in the psychological area (mood, social behavior, etc.)

Many of the patients with head injury due to accident an those with the diagnosis of post concussive syndrome (also known in neurology as diffuse encephalopathy ) may present chronic pain. This is in part due to the polytraumatic condition of these patients. Although we have to mention in here that many patients with diagnosis of chronic pain not due to head injury may accomplish the DSM IV criteria for post concussive syndrome (Iverson & McCracken, 1997) adding an important difficulty to the diagnosis work.

We certainly believe that it exists a wide disregard among the neuropsychology professionals about the categories and peculiarities of pain as well as about its consequences. Also we believe it currently exists an emptiness in what it is about the neuropsychological sequelae of chronic pain, not only related to attention deficits but in general.

There are different diagnostic categories or classifications of pain where chronic pain represents one of the most complex and hard to treat.

One proper definition of pain would be that one that the International Association for the study of pain (IASP) proposes. IASP defines pain as � one sensorial and emotional unpleasant experience with current or potential tissue damage or described in terms of such a pain� this concept is quite open and it allows the inclusion of complaints or experiences of pain with physical damage and those that may produce pain if this damage lasts longer. But it also allows the inclusion of those kind of pain experiences that exist with absence of current or potential physical damage. This is because as IASP there is no way to differentiate this type of pain from that one with a clear physiological cause since pain is a subjective experience.

Pain can be classified in different categories based on its physiopathogenesis, symptomathology mechanisms, etc.

They are some causes of pain in head injury patients as heterothopic ossification, denervation, complex sympathetic dystrophy, disuse, etc. that can be easily identified. But it is not our objective to focus on the head injury sequelae and refer to pain as one more of them. We prefer to focus on the concept of pain , the different categories of pain and specially on chronic pain.

We present some of the basic ideas currently accepted for the classification of pain according to IASP.

1.1. Acute Pain.

This concept refers to that pain that is caused by noxious stimuli coming from wounds or skin diseases, somatic structures or visceral or to tissue or visceral dysfunction . Acute Pain is usually limited in time and it produces a cascade of endocrine and physiological events since it uses to mean a signal of alert from the organism to tell us that something is wrong. Long term Acute Pain may produce noxious consequences because of these reasons. It is true that psychological and psychopathological issues may have a role in pain, this is not common in acute pain.

1.2. Chronic Pain.

If the stimular conditions, illness or another possible cause of pain are prolonged in time, it may originate what is known as chronic pain. Chronic pain produces physiological, psychological and behavioral effects, extending its consequences to the patient relatives and. Characteristics of chronic pain are different to that ones from previous type because here the intensity and the endocrine events are not present.

The frequent impossibility for inhibition of pain in these patients produces on them certain levels of physical inactivity with consequences such as muscle loss by disuse, bone problems, etc..

The neurons located in the grey periaqueductal substance surrounding the brain aqueduct of the mesencephalus may play a key role in the modulation of pain perception (Martin, H., 1997). It is precisely in this area where the descendent pain inhibition system originates.

After receiving complex codification commands coming from dyencephalic and encephalic structures, grey periaqueductal substance neurons project to the raphe nucleus in bulb. Neurons in nucleus of raphe employ serotonin (5HT) as neurotransmitter projecting towards the dorsal horn of the spinal cord. Serotonin suppresses the transmission of pain in the dorsal horn inhibiting the upper projection neurons which send noxious perceptive information to cortex .

So these paths would be influenced in chronic pain conforming a nosological entity and not an isolated symptom like in the case of acute pain.

They may be present also other consequences in chronic pain such as depression, anxiety, sexual dysfunction, etc.

1.3. Somatic Pain.

It is that pain which has origin in any part of the body which is not part of the central or peripheral nervous system. So all those originated in muscles, skin, bones or visceral. This last one is more difficult to describe or localize compared to those with origin in skin, bones or muscles.

1.4. Neuropatic Pain.

It is the pain originated in the central or peripheral nerve paths opposite to somatic pain.

This kind of pain may exist in absence of evident noxious stimulus and its localization can be specific or diffuse with symptoms ranging from burning sensation, exaggeration to generalization to painful perception of any stimulus. IASP provide a classification of terms used to define the different types of painful sensations.

1.5. Psychogenic Pain

That pain related to psychopathological basis and it uses to be exagerated.

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