Concept of disease
In general, disease is perceived as a disharmony (or imbalance) in the functions or interactions of yin, yang, qi, xu?, zang-fu?, meridians etc. and/or of the interaction between the human body and the environment.
Therapy is based on which “pattern of disharmony” can be identified.Thus, “pattern discrimination” is the most important step in TCM diagnosis.  It is also known to be the most difficult aspect of practicing TCM. In order to determine which pattern is at hand, practitioners will examine things like the color and shape of the tongue, the relative strength of pulse-points, the smell of the breath, the quality of breathing or the sound of the voice.For example, depending on tongue and pulse conditions, a TCM practitioner might diagnose bleeding from the mouth and nose as: “Liver fire rushes upwards and scorches the Lung, injuring the blood vessels and giving rise to reckless pouring of blood from the mouth and nose.”  He might then go on to prescribe treatments designed to clear heat or supplement the Lung.
Disease entities
In TCM, a disease has two aspects: “bìng” and “zhèng”. The former is often translated as “disease entity”, “disease category”,”illness”, or simply “diagnosis”. The latter, and more important one, is usually translated as “pattern” (or sometimes also as “syndrome”). For example, the disease entity of a common cold might present with a pattern of wind-cold in one patient, and with the pattern of wind-heat in another.
From a scientific point of view, most of the disease entitites (病, pinyin: bìng) listed by TCM constitute mere symptoms. Examples include headache, cough, abdominal pain, constipation etc.
Since therapy will not be chosen according to the disease entity but according to the pattern, two patients with the same disease entity but different patterns will receive different therapy. Vice versa, patients with similar patterns might receive similar therapy even if their disease entities are different. This is called 异病åŒæ²»ï¼ŒåŒç—…异治 (pinyin: yì bìng tóng zhì, tóng bìng yì zhì, “different diseases, same treatment; same disease, different treatments”).
Patterns
In TCM, “pattern” (è¯, pinyin: zhèng) refers to a “pattern of disharmony” or “functional disturbance” within the functional entities the TCM model of the body is composed of. There are disharmony patterns of qi, xuÄ›, the body fluids, the zà ng-fÇ”, and the meridians. They are ultimately defined by their symptoms and “signs” (i.e., for example, pulse and tongue findings).
In clinical practise, the identified pattern usually involves a combination of affected entities (compare with typical examples of patterns). The concrete pattern identified should account for all the symptoms a patient has.
Six Excesses
The Six Excesses (å…æ·«, pinyin: liù yÃn, sometimes also translated as “Pathogenic Factors”, or “Six Pernicious Influences”; with the alternative term of å…邪, pinyin: liù xié, – “Six Evils” or “Six Devils”) are allegorical terms used to describe disharmony patterns displaying certain typical symptoms. These symptoms resemble the effects of six climatic factors. In the allegory, these symptoms can occur because one or more of those climatic factors (called å…æ°”, pinyin: liù qì, “the six qi”) were able to invade the body surface and to proceed to the interior. This is sometimes used to draw causal relationships (i.e., prior exposure to wind/cold/etc. is identified as the cause of a disease), while other authors explicitly deny a direct cause-effect relationship between weather conditions and disease,  pointing out that the Six Excesses are primarily descriptions of a certain combination of symptoms  translated into a pattern of disharmony.  It is undisputed, though, that the Six Excesses can manifest inside the body without an external cause.  In this case, they might be denoted “internal”, e.g., “internal wind”  or “internal fire (or heat)”.
The Six Excesses and their characteristic clinical signs are:
- Wind (风, pinyin: fÄ“ng): rapid onset of symptoms, wandering location of symptoms, itching, nasal congestion, “floating” pulse; tremor, paralysis, convulsion.
- Cold (寒, pinyin: hà n): cold sensations, aversion to cold, relief of symptoms by warmth, watery/clear excreta, severe pain, abdominal pain, contracture/hypertonicity of muscles, (slimy) white tongue fur, “deep”/”hidden” or “string-like” pulse, or slow pulse.
- Fire/Heat (ç«, pinyin: huÇ’): aversion to heat, high fever, thirst, concentrated urine, red face, red tongue, yellow tongue fur, rapid pulse. (Fire and heat are basically seen to be the same)
- Dampness (湿, pinyin: shÄ«): sensation of heaviness, sensation of fullness, symptoms of Spleen dysfunction, greasy tongue fur, “slippery” pulse.
- Dryness (燥, pinyin: zaò): dry cough, dry mouth, dry throat, dry lips, nosebleeds, dry skin, dry stools.
- Summerheat (暑, pinyin: shǔ): either heat or mixed damp-heat symptoms.
Six-Excesses-patterns can consist of only one or a combination of Excesses (e.g., wind-cold, wind-damp-heat). They can also transform from one into another.
Typical examples of patterns
For each of the functional entities (qi, xuĕ, zà ng-fǔ, meridians etc.), typical disharmony patterns are recognized; for example: qi vacuity and qi stagnation in the case of qi; blood vacuity, blood stasis, and blood heat in the case of xuĕ;  Spleen qi vacuity, Spleen yang vacuity, Spleen qi vacuity with down-bearing qi, Spleen qi vacuity with lack of blood containment, cold-damp invasion of the Spleen, damp-heat invasion of Spleen and Stomach in case of the Spleen zà ng; wind/cold/damp invasion in the case of the meridians.
TCM gives detailed prescriptions of these patterns regarding their typical symptoms, mostly including characteristic tongue and/or pulse findings. For example:
- “Upflaming Liver fire” (è‚ç«ä¸Šç‚Ž, pinyin: gÄnhuÇ’ shà ng yán): Headache, red face, reddened eyes, dry mouth, nosebleeds, constipation, dry or hard stools, profuse menstruation, sudden tinnitus or deafness, vomiting of sour or bitter fluids, expectoration of blood, irascibility, impatience; red tongue with dry yellow fur; slippery and string-like pulse.
Basic principles of pattern discrimination
The process of determining which actual pattern is on hand is called è¾©è¯ (pinyin: bià n zhèng, usually translated as “pattern diagnosis”,  “pattern identification” or “pattern discrimination”). Generally, the first and most important step in pattern diagnosis is an evaluation of the present signs and symptoms on the basis of the “Eight Principles” (八纲,pinyin: bÄ gÄng). These eight principles refer to four pairs of fundamental qualities of a disease: exterior/interior, heat/cold, vacuity/repletion, and yin/yang. Out of these, heat/cold and vacuity/repletion have the biggest clinical importance. The yin/yang quality, on the other side, has the smallest importance and is somewhat seen aside from the other three pairs, since it merely presents a general and vague conclusion regarding what other qualities are found. In detail, the Eight Principles refer to the following:
- Exterior (表, pinyin: biaÇ’) refers to a disease manifesting in the superficial layers of the body – skin, hair, flesh, and meridians. It is characterized by aversion to cold and/or wind, headache, muscle ache, mild fever, a “floating” pulse, and a normal tongue appearance.
- Interior (里, pinyin: lÇ)refers to disease manifestation in the zà ng-fÇ”, or (in a wider sense) to any disease that can not be counted as exterior. There are no generalized characteristic symptoms of interior patterns, since they’ll be determined by the affected zà ng or fÇ” entity.
- Cold (寒, pinyin: hà n) is generally characterized by aversion to cold, absence of thirst, and a white tongue fur. More detailed characterization depends on whether cold is coupled with vacuity or repletion.
- Heat (çƒ, pinyin: rè) is characterized by absence of aversion to cold, a red and painful throat, a dry tongue fur and a rapid and floating pulse, if it falls together with an exterior pattern. In all other cases, symptoms depend on whether heat is coupled with vacuity or repletion.
- Vacuity (虚, pinyin: xÅ«) often referred to as “deficiency”, can be further differentiated into vacuity of qi, xuÄ›, yin and yang, with all their respective characteristic symptoms. Yin vacuity can also be termed “vacuity-heat”, while yang vacuity is equivalent to “vacuity-cold”.
- Repletion (实, pinyin: shÃ) often called “excess”, generally refers to any disease that can’t be identified as a vacuity pattern, and usually indicates the presence of one of the Six Excesses, or a pattern of stagnation (of qi, xuÄ›, etc.). In a concurrent exterior pattern, repletion is characterized by the absence of sweating.  The signs and symptoms of repletion-cold patterns are equivalent to cold excess patterns, and repletion-heat is similar to heat excess patterns.
- Yin and yang are universal aspects all things can be classified under, this includes diseases in general as well as the Eight Principles’ first three couples.  For example, cold is identified to be a yin aspect, while heat is attributed to yang.  Since descriptions of patterns in terms of yin and yang lack complexity and clinical practicality, though, patterns are usually not labelled this way anymore.  Exceptions are vacuity-cold and repletion-heat patterns, who are sometimes referred to as “yin patterns” and “yang patterns” respectively.
After the fundamental nature of a disease in terms of the Eight Principles is determined, the investigation focuses on more specific aspects.  By evaluating the present signs and symptoms against the background of typical disharmony patterns of the various entities, evidence is collected whether or how specific entities are affected.  This evaluation can be done
- in respect of the meridians (ç»ç»œè¾©è¯, pinyin: jÄ«ng-luò bià n zhèng)
- in respect of qi (气血辩è¯, pinyin: qì xuÄ› bià n zhèng)
- in respect of xuÄ› (气血辩è¯, pinyin: qì xuÄ› bià n zhèng)
- in respect of the body fluids (津液辩è¯, pinyin: jÄ«n-yÄ— bià n zhèng)
- in respect of the zà ng-fÇ” (è„腑辩è¯, pinyin: zà ng-fÇ” bià n zhèng) – very similar to this, though less specific, is disharmony pattern description in terms of the Five Elements [五行辩è¯, pinyin: wÇ” xÃng bià n zhèng])
There are also three special pattern diagnosis systems used in case of febrile and infectious diseases only (“Six Channel system” or “six division pattern” [å…ç»è¾©è¯, pinyin: liù jÄ«ng bià n zhèng]; “Wei Qi Ying Xue system” or “four division pattern” [å«æ°”è¥è¡€è¾©è¯, pinyin: weì qì yÃng xuÄ› bià n zhèng]; “San Jiao system” or “three burners pattern” [三角辩è¯, pinyin: sÄnjiaÅ bià n zhèng]).
Considerations of disease causes
Although TCM and its concept of disease do not strongly differentiate between cause and effect, pattern discrimination can include considerations regarding the disease cause; this is called ç—…å› è¾©è¯ (pinyin: bìngyÄ«n bià n zhèng, “disease-cause pattern discrimination”).
There are three fundamental categories of disease causes (ä¸‰å› , pinyin: sÄn yÄ«n) recognized:
- external causes: these include the Six Excesses and “Pestilential Qi”.
- internal causes: the “Seven Affects” (七情, pinyin: qì qÃng, sometimes also translated as “Seven Emotions”) – joy, anger, brooding, sorrow, fear, fright and grief. These are believed to be able to cause damage to the functions of the zà ng-fú, especially of the Liver.
- non-external-non-internal causes: dietary irregularities (especially: too much raw, cold, spicy, fatty or sweet food; voracious eating; too much alcohol), fatigue, sexual intemperance, trauma, and parasites (虫, pinyin: chóng).
