Clinical Characteristics of Pain

Pain has been defined as a specific feeling that protects from noxious stimuli. Pain is, however, not a single feeling. It is rather a group of distinct feelings, each of which has clinical character of its own. Thus pain of the skin is different from pain of the muscles. Each type is related to a definite group of tissues.

To make a homeopathic prescription for painful disorder and the patient presented with pain as only the symptom one must know all the qualities of pain e.g. location, sensation, modality, concomitant and the radiation of pain. Many of the times physician need to know the site of injury for further treatment purpose but patient does not know or tell. Other than this the sensation are often confusing because of the regional language and knowledge to define the sensation of pain by the patient. In nut-shell to draw a purposeful prescription knowledge of the clinical character of pain is essential.

Severity:

Patient's personality and surroundings influences much the general level of severity of a pain. So the level of severity does not predict much to draw any reliable conclusion for diagnostic or prescribing purpose. The examination of the relative sensitivity of tissues is more useful. Not all tissues are equally sensitive. Some, like cornea, are exposed to injury, and yet the effects can be serious even though the injury be slight. These tissues, as may be expected, have a high degree of sensitivity; but the sensitivity of ordinary tissues is much lower. It would be very inconvenient if the sensitivity of all tissues were high. When the injury is so mild as not to be of any consequence it does not reach consciousness. On the other hand, if the stimulus, even though mild, persists too long or if the tissue is still suffering from the after effects of a previous injury, further damage of any degree can be dangerous and the threshold of pain is then lowered. The sensitivity of a tissue is not a constant, but a variable that changes with the previous history of the injured tissue.

Thus if the skin is damaged in any way there develops after a short interval a diffuse area of tenderness which surrounds the site of injury. This area is hypersensitive to stimuli of heat, cold, pressure, etc., that from there degree would not normally be enough to produce pain. This hypersensitivity is limited specifically to the organs of pain; for example, the organs of touch are not affected, as can be tested by Fry's hairs. The central mechanism of this hyperalgesia is ultimately segmental, but the nerve distribution within the skin is such that the area of tenderness around the site of injury follows a geometrical, not a segmental pattern, being concentrical around the injured spot. It is never referred to a distance.

In the deeper tissues hypralgesia occurs also. The pain will be diffuse which may mislead as to the real site of injury. The distribution follows a segmental pattern not the geometrical, and can even be referred to a distance. Thus deep tenderness in diaphragmatic pleurisy may accompany pain over the neck and shoulder.

Site of Pain:

The power to locate the site of injury from the pain that is felt depends upon the type of tissue injured. It is perfect on the cutaneous surface, but gets progressively more defective the deeper the tissue.

Quality of Pain:

Quality is the distinctive character of a sensation. We always describe it by comparing it with a familiar pain or sensation. We use as terms of comparison a familiar pain which is related to some part of the body, as when we say that the pain feels like a tummy ache; or we compare pain with that which is related to a function, as when someone says it is throbbing pain. Much more commonly we make comparison with a pain that is provoked by a familiar stimulus, as we call a pain "burning" because the same type of pain is produced by a burn.

The quality of pain is a function of the injured tissue not the stimulus for example the injection of 0.5 c.cm. of 6% hypertonic saline produces burning in the skin, aching in the muscles, and pain of a different quality in the subcutaneous tissue of the forearm.

Somatic Pain :

At least 3 types of pain can be distinguished :

• Surface pain, from the cutaneous and mucosal surface
• Sub surface or intermediate pain from the subcutaneous tissues (where there are thin), from the submucousae, and from the adjacent structures when the subcutaneous tissue is very thin.
• Deep pain, from muscles and from all the other sensitive deep tissue in general.

Surface Pain

If pain from the skin is very short it is pricking, if prolonged it is burning; the difference between the two being only of duration, not the quality. Pricking can be elicited from exactly the same spot and by the same stimuli that give burning when the injury is prolonged. pricking and burning are the only senasation of pain from normal skin. They are generally modified by concomitant subcutaneous pain or by touch, temperature sense, etc., but if these feelings are eliminated the skin is unable to respond to any short of injury except by pricking or burning. Burning is the sensation which we associate with excesive heat, but it is defenetly not the response of temperature organs to the excess of heat. Excessive heat produces burning because it produces prolonged injury and stimulates the cutaneous organs of the pain. Also cold, if intense enough to cause injury, produce burning, as can be evidenced by prolonged immersion of a finger in a freezing mixture, by a cold wind, or by chilblains. Pricking or burning is absent in injury to the skin only if the cutaneous organs of pain are not functioning on account of destruction or otherwise. On the other hand, if the lesion is only superficial, as in mild burn no other pain will be added.

Itching

Injury to the skin can also produce itching, but for itching to appear the stimulus must act on a skin that is hyperalgesic. Itching is not elicited from a normal skin. In a skin that has been already injured, as in dermatitis, it can be provoked even by very slight added injury, such as scratching, the application of ointments, changes of temperature, etc. the quality of itching cannot be distinguished from the pricking - like pain which is produced by droplets of strong acids or of other irritants if they fall on the skin in size so minute as not to be felt. It is suggested that itching is only a variety of surface pain which is completely free from any other sensation and which occurs in skin that is hyperalgesic from a previous injury.

Other Characters of Cutaneous Pain

The functions of surface pain are obviously directed towards providing enough information about the offending stimulus to make adequate defensive reactions possible. In fact, all its characters tend to promote accuracy ; the pain is very well located; it is localized and never referred to a distance; the power of discrimination is very good. The protective reflexes provoked by the injury are all directed with considerable precision towards the elimination of the stimulus or towards the withdrawal of the injured part from the danger. Typical are the scratch and the flexor reflexes. If the stimulus is adequate there is an added systemic reaction which invigorates the mind and the body and enables the individual to face the danger. Sympathetic activity is then increased; the mind is on the alert and emotions of anger, rage, fear, etc may appear. These reactions are sometimes provoked purposely by inducing surface pain. Thus they occur when we stimulate horses by whipping or during certain forms of treatment of a fainting fit.

Pain from Mucosae:

Not all the mucasae are sensitive. Those that are distant from injury of external origin are insensitive. When, however, a mucosa is sensitive its pain is pricking or burning, as can be expected when we consider that a mucosa is a surface. Itching, pricking, and burning are familier results of injury to the stratified mucosae of the conjunctiva, mouth, throat, anal canal, urethra, labia, and lower vagina. Whatever the stimulus, the pain is alwayas of the same quality. Thus burning in the mouth occurs whether the injury is due to hot food or to a chemical irritant, catarrhal inflammation, ulcer or atrophy from a deficiency disease.

The oesophageal mucosa is normally insensitive to the presence of gastric juice, which regurgitates even during normal digestion. When, however the mucosa is injured from any cause it becomes sensitive to further injury. Its pain is then burning. The pain occurs during the ingestion of irritants or during digestion when acid juice regurgitates. It is then spoken of as heartburn. It is diffuse, and is located vaguely behind the lower part of the sternum.

The pain of cervical erosion is not burning; but the mucosa of the cervix is so much adherent to the underlying tissues that the pain of cervical erosion is probably due to these subjacent tissues. The mucosa itself is probably insensitive; it does not respond to pin prick. Equally the pain of nasal mucosa, when provoked by ordinary stimuli, is due chiefly to the underlying periostium to which the thin simple mucosa is adherent. If stimuli that act only very superficially are used as in the inhalation of ammonia or on the instillation of hypertonic drops, the pain elicited is purely pricking or burning. The nasal sinuses and the middle ear are usually described as having a sensitive mucosa; but probably the mucosa is insensitive and pain which is felt is periosteal. Pain from the larynx is pricking or burning.

The transitional mucosa of the urinary bladder also gives pricking or burning pain but its behavior is peculiar.

Subcutaneous or Intermediate pain:

Pain of subcutaneous surface is of different character from those of deep pain especially if the subcutaneous tissues are thin, as over the fore arm, tibia, or over the knuckles, the outer fibers of the tendoachillis, and the fibrous web two fingers. however where the subcutaneous tissues are thick, as in the female mammary region, pain of inner strata is not described as different in quality from deep pain.

The pain is somewhat diffuse, but its diffusion is always limited to a narrow zone around the injury. It gets wider when the tissue is deep, but it is not referred to a distance.

Deep Pain:

Pain from deep tissues has an aching quality. It is common to muscles and to all other sensitive deep tissues in general.

It is non- discriminative. It is unable to give the information about stimulus and source of pain. It starts late and persists long. The pain is always very diffuse. It is impossible, from a deep tissue, to get pain which is felt only at the site of injury. The pain radiates to distance and this radiation is often extensive. There are several factors which determine whether the pain remains local or radiates extensively. The severity of the injury is important. The time-interval after the injury is important too. When adaptation to pain starts after a variable interval, the pain becomes restricted to a narrow area; but subsequent injury of any nature, or even active muscular exercise, can not only re-exacerbate the pain but also make it extend to some distance. A very important factor is the depth of injured tissue. The deeper the tissue the greater is the tendency of pain to radiate extensively. The relation of the injured tissue to structure of vital importance, as the spine, is perhaps also important. The nearer the tissue to such structures the more the pain radiated. The radiated pain can be as intensive at a distance as over the site of injury. Possibly, pain that is referred from certain viscera is badly located for similar reasons.

The reflexes that accompany deep pain, far from provoking brisk defensive movements, produce tonic contractions and quiescence. They aim more at resting the injured part and protecting it from subsequent injury than at eliminating the offending stimulus. The contraction is slow in onset and gets maximal only after a considerable interval. Sometimes the rigidity is slight and passes unobserved, the patient limiting his movements more from fear of exacerbating the pain than from inability to move on account of spasm. When, however, the injury is appropriately located as near a joint, near a cavity, or near a vital organ, the spasm may be such as to resist even deep anaesthesia and hamper operative interventation. It may be localized , but when severe it may form a definite barrier around the greater part or the whole of the injured segment, and may even occur at a distance from the injury. Thus the cremaster may contract when the injury is located in the spine.

The general reactions that are associated with deep pain tend equally to inhibit activity. Far from being invigorating, they cause mental and physical depression, with diminished knee jerks, low blood pressure etc. if the injury is severe, especially if it is diffuse and located within the trunk or very near to it. The full picture of "nervous" shock appears.

The Segment:

However diffuse or referred deep pain may be, its distribution follows always a segmental pattern. Within the affected segment the direction of the diffusion of deep pain is determined more by the level of the segment than by the situation of the injured spot in the segment. This extension of pain in an anterior or posterior direction occurs the same whether the pain is visceral or somatic in origin.

Visceral Pain :

The viscera lies, as a rule, so deep within the segments that they are well protected and do not therefore respond to the stimuli that provoke pain ordinarily in the somatic tissues. Many viscera are completely insensitive and any pain that is associated with them is caused by an extension of the lesion to adjacent tissues, as to the parietal peritoneum or to the retroperitaneum. Other viscera are sensitive, but their stimuli …..be appropriate to them, and their pain has the same characters and is probably furthered by the same mechanism as somatic pain. Embryologically these viscera are intimately connected with the somatic tissues. They arise entirely from the mesoderm, from each side of the segment; they are paired, or have been paired during some period of their embryonic life. Examples are the kidney and the heart.

There is still another group of viscera. These are hollow organs which have never been paired, but have had always a mesial attachment and have included ectoderm in their cavities. Pain from these organs has distinct characters. The pain diffuse but, even when maximal it remains always mesial and never extends beyond the abdominal walls to the limbs, its distribution is segmental. It is referred to the level from which the viscus migrates in embryological development. It is epigastric for the stomach, duodenum and gallbladder; umbilical for the small intestine appendix; hypogastric for the colon and urinary bladder. Pain from the rectum is felt vaguely about the site of the viscus.

Conclusion:

If we go through the generalities part of the Kent's Repertory we found much of subrubrics under the main rubric pain. They are based on a definite group of tissues e.g. Pain, bones; Pain, periosteum; Pain, glands etc. or the type e.g. Brning, biting, benumbing, constricting etc. From their clinical characters we can distinguish types of pain each of which is related to a definite group of tissues.