2.2 Processes of disease
Estimated time for chapter: 30 minutes.
This chapter introduces some ideas that lie at the foundation of how conventional medicine starts to classify disease. Within conventional medical thought, diseases can be classified according to different criteria. All systems of classification share the potential benefit of clarifying those features that disparate diseases may have in common, and thus aiding communication about these diseases.
Diseases may be classified according to cause, and this is known as ‘classification by aetiology’. Understanding the language of aetiology is an essential prerequisite if the prevention of disease is to be considered. A classification system that focuses on the disease mechanisms (pathogenesis of disease) is a prerequisite for beginning to understand which treatments may be most effective for different diseases and also for predicting outcome (prognosis).
‘Aetiology’, literally meaning ‘the study of causes’, is the term used to describe the cause of disease. From a conventional medical viewpoint, the cause of disease can be simplified into a few distinct categories, including:
The terms ‘idiopathic’ and ‘essential’ may be ascribed to diseases of unknown cause (e.g. idiopathic thrombocytopenic purpura and essential thrombocythaemia) (see Q 2.2a-1).
‘Pathogenesis’ (literally ‘the birth of disease’) is the term used to describe the pathology of how disease develops. The diverse forms of the disease process can be grouped into seven broad categories:
From the perspective of the study of clinical medicine, classification of the processes of disease is important because it generates principles of causation of disease that can then be applied to all diseases. For example, if the process of inflammation is understood, then this will aid in the study of any one of the diseases that involves inflammation, such as arthritis, dermatitis, meningitis and pneumonia. Because the understanding of these basic processes of disease is fundamental to the study of the pathology of all diseases, they are explored in some depth in this text. The topics of inflammation, abnormal immune mechanisms, thrombosis, embolism and infarction, and tumours (cancer) are the subjects of the next four chapters.
Degeneration is the result of ageing. In general, ageing involves cell loss and atrophy of tissues. Rapidly regenerating active tissue may become replaced with tough, fibrous, less-active tissue, and organs may cease to function as effectively. Deformities (e.g. of skin, joints or bones) become commonplace. Degenerative diseases will be discussed in later chapters according to the physiological system which they affect.
The category of metabolic abnormality embraces all diseases that develop when the homeostatic function for metabolism (the chemical processes that go on continuously in living cells) becomes imbalanced. Again, the metabolic disorders are discussed throughout the text according to the physiological system which they affect.
An understanding of the processes of disease can also aid thinking about disease from the perspective of another medical system. If it is possible to consider each process of disease in terms of corresponding pathological descriptions described in another medical system, then it is possible to take these correspondences and use them to help describe pathological processes in all manner of diseases. For example, inflammation always involves the generation of redness and heat in tissues. According to Chinese medicine, redness and local heat always corresponds to the Pathogenic Factor of Heat. Therefore, it would be reasonable to conclude that all inflammatory diseases will be described, amongst other things, in terms of Heat in Chinese medicine. In this chapter, all the processes of disease are also interpreted in terms of Chinese medicine, and this will provide the foundation for the Chinese medicine interpretations of all the individual diseases described later in the text (see Q2.2a-2).
In summary, it cannot be overstated how much the understanding of the basic processes of disease can enrich the understanding of conventional pathology and how it might relate to another medical system such as Chinese medicine.
Information Box 2.2a-I Processes of disease: comments from a Chinese medicine perspective
As a general introduction, it is important to explain the rationale for comparing the conventional view of the processes of diseases with a Chinese medicine understanding of pathology. As stated in the text, in the study of clinical medicine classification of the processes of disease is important because it generates principles of causation of disease, which can then be applied to all diseases. For example, an understanding of the process of inflammation will aid in the study of any disease that involves inflammation, such as arthritis, dermatitis, meningitis and pneumonia.
The important aspect of this system of classification is that, although the understanding of conventional processes would have involved knowledge that would not have been known to the ancient Chinese, the manifestations of the processes in signs and symptoms are consistent within each process. It is these that are the bridge between the two systems of medicine.
Inflammation will always have characteristics of heat and swelling, and degeneration will always involve a drying and withering of tissue. As observable phenomena, these would form the basis for making a diagnosis in Chinese medicine. However, the way in which the heat and swelling is generated in each individual case does not share the same consistent internal process as understood in the conventional view, and looking for parallels of process is a trap for the unwary.
When a patient presents with a condition that results from one or more of the seven processes of disease, it can reasonably be expected that the symptoms and signs normally associated with those processes are evident. The meaning and importance of the signs and symptoms can then be assessed within the entirely different understanding of the manifestation of symptoms and signs described in Chinese medicine. What this means is that the symptoms and signs of the conventionally described processes of disease will help point to the Chinese medicine syndromes that might be expected to be discerned in any medical condition, first assuming the underlying process of disease is recognised.
Inflammation is a basic response to tissue damage that results in increased blood flow to the tissues, swelling from increased tissue fluid, pain as a result of release of irritant cell contents and loss of function of the body part as a result of pain and swelling. Together these factors result in the five characteristics of inflamed tissue described in medicine as redness, swelling, heat and pain (or in Latin as rubor, tumour, dolor, calor), and loss of function.
In Chinese medicine the characteristics of redness and heat would automatically point to Heat. The excess tissue fluid would often be associated with an underlying Pathogenic Factor such as Damp, especially if there was any oozing of liquids or the swelling was considerable. The swelling in a clearly defined area would itself point to local stagnation, usually of Qi or Blood, and the character of the pain would indicate which. If inflammation is confined to one peripheral body part, the term ‘Bi Syndrome’ may be applied in Chinese medicine, as this describes localised manifestations of Pathogenic Factors, particularly in the region of the joints.
Tumours result from excessive and inappropriate overgrowth of tissue cells. The underlying problem from a conventional medicine perspective is that the genetic control of cell multiplication has become disordered and the immune system has failed to recognise and control the growth of these disordered cells.
In Chinese medicine, substantial masses that do not move easily are usually regarded as manifestations of either Phlegm or Blood Stagnation (or sometimes a combination of both). Blood Stagnation is characterised by hardness and intense boring pain with violaceous colour changes. Phlegm is more often associated with numbness, and will usually develop against a backdrop of Heat and Damp, which will manifest in other signs and symptoms. For long-standing masses to develop there is often a pre-existing state of deficiency of Qi, as it is only healthy Qi moving freely that prevents the development of Stagnation and Phlegm. However, some masses can manifest against a background of good Upright Qi, the strength of which is often used to determine priorities in treatment.
Abnormal immune mechanisms fall into two broad categories: those involving an insufficient response to infection, and those involving inappropriate responses, where there is hypersensitivity to specific stimuli or the misrecognition of the body’s own cells as a threat.
In Chinese medicine, the functions of a healthy immune system are reflected in the concept of Healthy Upright Qi. The foundation of Healthy Upright Qi lies in Kidney Essence, and both are essential in maintaining Wei Qi. Some of the patterns of abnormal immune responses, for example, type I allergic hypersensitivity, are reflected in recognised patterns of disruption of Wei Qi, and suggest deficiencies either in Wei Qi or in the underlying Kidney Essence itself. Others, for example in multisystem autoimmune disease, present much more of a pattern of Full Pathogenic Factors against a background of long-term deficiency of Upright Qi or Kidney Essence.
Excessive blood clotting in the body is characterised by intense pain, coldness, violaceous coloration and loss of function. All these symptoms are associated with what is described in Chinese medicine as Stasis of the flow of Blood, with associated Stagnation of Qi in the affected tissues.
In conventional medicine, degeneration of tissues involves excessive cell death, poor healing responses and the formation of less vital tissues, with excessive fibrous tissue and deposits of substances such as calcium salts that impede healthy function. The resulting tissues tend to be less springy and soft and resilient, and also may manifest with deformities (‘lumps and bumps’).
In Chinese medicine language, all these changes, if seen across large areas of the body, would be primarily described in terms of broad deficiencies of Yin and Yang. More particularly, they are linked with a deficiency rooted in the Kidneys, and are characteristic of the ageing process as Kidney Essence depletes. The deposits and deformities are evidence of a widespread lack of flow of Qi, leading to an accumulation of Pathogenic Factors such as Phlegm and Damp and Blood Stagnation. If these are localised, there may be evidence of local Qi or Blood Stagnation impairing the flow of Qi to a part of the body.
In conclusion, degeneration of a body part might be described as evidence of Deficiency or Yin and/or Yang, in particular of Kidney Qi/Essence, leading to an accumulation of Phlegm/Damp and other Pathogenic Factors.
The metabolic diseases are complex and have diverse symptoms depending on the fundamental abnormality. Most metabolic diseases will be manifest in the function of all the body tissues and so reflect a fundamental and profound state of imbalance.
Chinese interpretations of metabolic disease will be equally complex, and are likely to describe deep deficiency. However, in Chinese medicine a profound and prolonged deficiency can often result in full Pathogenic Factors, which create complex patterns of signs and symptoms. As in conventional medicine, however, the effects are likely to be widespread in the system.
A genetic abnormality may affect every cell in the body (if present from the time of conception), or may be the result of a developmental problem in the womb and thus affect some body parts and not others. From a conventional medicine perspective, there is no doubt that a congenital abnormality will compromise the health of the child and, unless carefully managed, is likely to affect the growth and development of the affected child.
The ancient Chinese interpreted congenital disease (i.e. a condition present from the time of birth) as a deficiency of Kidney Essence (Jing). To the Chinese, Kidney Essence was what determined a person’s constitutional strength and is fundamental to healthy growth and development. Kidney Essence underlies the health of all the organs, and so more specific imbalances will often be present as the visible sequelae of the congenital disorder (e.g. of Spleen and Lung Qi in cystic fibrosis).
In conclusion, a congenital problem might be described as evidence of Primarily Jing deficiency, but may be described as a specific organ deficiency, depending on where the underlying genetic defect manifests.
Self-test 2.2a Processes of disease
Estimated time for chapter: 90 minutes.
‘Inflammation’ is the term used to describe a complex bodily response to damage. The word is derived from the Latin words meaning ‘to set on fire’, because two manifestations of inflammation are heat and redness. Two other important features are swelling and pain. These characteristics of inflammation have been familiar to doctors over many centuries. They were noted by the 1st century Roman medical encyclopaedist Celsus as calor (heat), tumour (swelling), rubor (redness), dolor (pain).
Inflammation has one other major characteristic in that it leads to ‘loss of function’ of the affected body part. Swelling and pain largely contribute to this loss of function. In mild disease, loss of function can be beneficial, as it encourages the patient to rest the inflamed area, and this should promote healing. For example, inflammation of the voice box (laryngitis) may give rise to discomfort and malaise. This means that the patient avoids talking, and may wish to rest in bed. Both these responses will promote healing.
In severe disease, the loss of function can jeopardise the health of the whole body, and is not necessarily so beneficial. For example, inflammation of the lining of the brain resulting from bacterial infection (meningitis) leads to swelling of the brain and carries the risk of coma and death.
When a body part is inflamed, it is often medically described by the suffix ‘-itis’. This suffix may be added on to the common name for the affected organ or, more usually, to the Latin term for the organ. Hence in tonsillitis, dermatitis, laryngitis, osteomyelitis and tendonitis we would expect to find inflammation of the tonsils, skin, larynx, bone marrow and tendons, respectively (see Q2.2b-1).
The trigger for inflammation is always tissue damage. When tissues are damaged, cells are ruptured and release their contents. The presence of cell contents in the extracellular space has a powerful effect on the immune system and the capillary cells. The released chemical contents of cells signal to the immune system and capillary cells that there is cell debris that needs removing, that repairs may need to be performed, and that there might be foreign bodies and infectious organisms to be eradicated. Their presence induces responses in immune and epithelial cells that bring about the inflammatory response, and thus begins the process of healing. The chemicals released include the prostaglandins, histamine, serotonin (5HT) and bradykinin.
A cardinal response in inflammation is that blood flow to the damaged area increases, a result of widening of the small blood vessels (vasodilatation). This response is termed ‘hyperaemia’ (literally meaning ‘more blood’). Hyperaemia leads to the increased warmth and redness that are characteristic of inflammation. Hyperaemia also contributes to tissue swelling.
Another response of the blood vessels to inflammatory chemicals is that gaps form between the epithelial cells of the vessels so that molecules and fluids move out of capillaries into the fluid surrounding the tissue cells. In this way important proteins such as antibodies and fibrinogen enter the site of the damage. This reaction, known as ‘exudation’, leads to the swelling that is characteristic of inflammation. Fibrinogen, one of the 12 clotting factors in the blood, is converted to fibrin once it enters tissue fluid, and in this way it forms a meshwork that contains the inflamed area and thus prevents the spread of any infection that may be present. Antibodies bind to foreign antigens at the site of the inflammation and so form immune complexes that are then engulfed by phagocytic cells such as neutrophils.
Various forms of leukocytes, which are the basis of the immune system, are attracted from the blood and the tissue fluid to the site of the damage by the chemicals (chemotaxins) that have been released as a consequence of the damage. Neutrophils are amoeba-like white cells that appear rapidly at the site of inflammation. These have the capacity to engulf and digest any material that presents foreign antigens in the form of an immune complex. In this process, the phagocytic cells may die, releasing their greenish cell contents. It is these discharged cell contents that contribute to the green colour of pus, which is usually only formed as a consequence of a heavily infected wound. Macrophages are slower moving, larger phagocytic cells, which after a few hours also enter the site of inflammation to engulf and digest cell debris, microbes and dead neutrophils.
If the bodily response of inflammation is sufficiently large, then interleukin-1, a chemical released by macrophages, can lead to an increase in the core temperature of the body. The fever that results leads to more efficient activity of phagocytes and also encourages the patient to rest. Fever is thus understood to be beneficial to the healing process in inflammation.
The chemicals released by damaged and inflammatory cells tend to irritate the local nerve endings, so leading to the acute pain and intense tenderness associated with inflammation (see Q2.2b-2 and Q2.2b-3).
In uncomplicated situations, the inflammatory process leads to removal of damaged cells, dirt and infectious organisms, and provides a clean environment for the process of wound healing. The redness, swelling, pain and heat resolve, function of the area is restored and healing is complete, with or without scar formation.
The resolution of inflammation may be hindered by a poor blood supply, the presence of a foreign body or as a response to certain organisms. In the case of chronic inflammation, after a time increasing numbers of lymphocytes get attracted to the area and the scar-tissue forming cells, the fibroblasts, are continually activated meaning excess scar tissue may be formed. The chronic skin ulcer described in Chapter 2.1b is an example of chronic inflammation. Tuberculosis (TB) is an example of an infection in which the slow-growing infectious organism Mycobacterium tuberculosis encourages a chronic inflammatory response and the formation of clusters of immune cells around foci of infection known as granulomas (see Q2.2b-4). These tiny clusters of immune cells are characteristic of this disease and are evidence to the pathologist of its ability to induce damaging chronic inflammation.
Information Box 2.2b-I Inflammation: comments from a Chinese medicine perspective
Redness and heat signify the presence of Heat in Chinese medicine. The characteristics of pain, with aversion to pressure, and a purplish discoloration suggest a degree of Blood Stagnation. In Chinese medicine, Blood Stagnation can lead to Heat, and Heat can be a cause of Blood Stagnation. Therefore, these Pathogenic Factors are inextricably interrelated in inflammation.
Excess tissue fluid and the swelling and oozing which result could be equated with the Pathogenic Factor of Damp. This may be localised or may be systemic, in which case there may well be underlying patterns of Spleen Deficiency.
Boils and abscesses occur when excess pus is formed and collects within the tissues at a site of inflammation. Abscesses are simply big boils; there is no clear-cut difference between the two. Pus is more likely to collect if a foreign body is present at the site of inflammation and also if certain ‘pyogenic’ organisms are present. The most common pyogenic organism to cause medical problems is Staphylococcus aureus, one of the many normal and healthy (commensal) skin bacteria.
A boil or abscess ideally heals by means of discharge of pus to the surface. For example, a stye (a boil of the edge of the eyelid) usually comes to a point after a few days and this then breaks open to release the pus and allow healing.
This ideal outcome is not always achieved. In some cases the pus does not discharge fully, and the channel leading from the pus to the skin does not heal fully, remains as a sinus that discharges pus long term. This can lead to long-term ill-health, as the body is always in a state of fighting infection. An infection in bone (osteomyelitis) can easily lead to sinus formation, because the bone is relatively protected from the immune system and thus chronic inflammation can easily develop in bone. This is a particular problem with shrapnel wounds in wartime, which may lead to a continual discharge of pus from the bone through a sinus to the skin.
When a sinus is formed, the discharge of pus can go two ways: into closely apposed organs (e.g. stomach and bowel, or bladder and bowel) so that a permanent channel is formed between them (fistula). This can have severe consequences. One common cause of a fistula is the inflammatory bowel disease Crohn’s disease. Diverticulitis of the bowel is another cause.
If the pus is not discharged at all it is eventually phagocytosed. This is a common occurrence with small boils (pustules) such as occur in severe acne. Instead of discharging fully, these form tender lumps that gradually become less painful. This form of healing is more likely to lead to scarring resulting from chronic inflammation, as fibrous tissue is formed to fill the cavity formed by the pus, and this can have severe cosmetic consequences (see Q2.2b-5).
The most appropriate medical treatment of boils and abscesses promotes natural resolution. Astringent medication in the form of hot packs (poultices) can be applied to the site of a superficial abscess to encourage the pus to discharge outwards.
Information Box 2.2b-II Boils and abscesses: comments from a Chinese medicine perspective
In Chinese medicine, boils and abscesses are manifestations of Damp and Heat, and in severe cases of Fire-Poison. Full resolution represents clearance of these Pathogens; therefore, poultices, lancing and drainage are energetically appropriate treatments that can facilitate full cure.
Antibiotics may actually suppress full cure in the conventional sense of the term, as the causative microorganisms may remain relatively protected from the drug deep within the walled-off centre of the abscess. From an alternative medicine perspective this outcome may be interpreted as suppression, as the root cause has not been treated directly (e.g. Spleen Qi Deficiency leading to poor health of the tissues). Nevertheless, there are situations in which antibiotic treatment is necessary to allow healing of an abscess while preventing the dangerous spread of infection (e.g. in a brain abscess).
An abscess that does not discharge, but instead resolves to form a hard painless lump under the surface of the skin, might be described in Chinese medicine in terms of accumulation of Phlegm, which is usually the consequence of the action of Heat on Damp.