Traditional Chinese Medicine (TCM) internal medicine is a clinical discipline that studies the patterns of differentiation and treatment of internal diseases based on TCM theories. TCM internal diseases can primarily be divided into two categories: external pathogenic diseases and internal injury diseases. Generally speaking, external pathogenic diseases refer to acute illnesses such as cold (shanghan), wind-heat (fengwen), summer-heat (shuwen), and damp-heat (shiwens), which are treated based on the six meridians, defensive qi, nutritive blood, and the three burners. Internal injury diseases include various diseases of the organs and meridians, primarily treated through differentiation based on the organs, qi, blood, body fluids, and meridians.
From a clinical guidance perspective, classification is generally based on etiology and pathogenesis. When using etiology as the basis for classification, it can be divided into two major categories: external pathogenic diseases and internal injury diseases. External pathogenic diseases are caused by external evils such as the six excesses; internal injury diseases are often caused by emotional disturbances, improper diet, overwork, and abnormalities in the generation and distribution of qi, blood, and body fluids, as well as their pathological metabolic products. In terms of pathogenesis classification, it can also be broadly divided into external pathogenic and miscellaneous diseases. Miscellaneous diseases are usually caused by internal injuries, and some conditions like cough, diarrhea, and dysuria caused by external pathogens are habitually classified under internal injury diseases due to their similar clinical manifestations to certain internal injury conditions.Although there are many types of internal injury miscellaneous diseases and their pathological changes are exceptionally complex and diverse, their pathological mechanisms are always related to the dysfunction of the organs and meridians and the abnormal generation and distribution of qi, blood, and body fluids.Therefore, internal injury miscellaneous diseases are mostly classified based on the physiological functions and pathological changes of different organs and the qi, blood, and body fluids, as well as the meridians. For example, the lungs govern qi and control respiration; thus, diseases with abnormal respiratory function due to lung dysfunction, such as cough and asthma, belong to lung system diseases. The heart governs blood vessels and also the mind; therefore, changes in the heart primarily involve disturbances in blood circulation and abnormalities in emotional and cognitive activities, such as arrhythmia, coronary atherosclerotic heart disease, and epilepsy. The spleen governs transportation and transformation, while the stomach is responsible for receiving and rotting food; if there is dysfunction in the spleen and stomach, it can lead to conditions such as gastritis, enteritis, and constipation. The liver governs the smooth flow of qi and is characterized by its strong nature; as the organ associated with wind and wood, dysfunction in the liver and gallbladder can lead to conditions such as hepatitis, liver cirrhosis, and cholecystitis, or liver yang transforming into wind, disturbing the head and causing dizziness and headaches. The kidneys store essence, govern reproduction, and control the five fluids; thus, any changes in the urinary and reproductive systems, such as impotence, premature ejaculation, nephritis, and urinary tract infections, are classified as kidney diseases. Additionally, conditions like rheumatoid arthritis and gout are due to the invasion of the limbs’ meridians and are classified as limb meridian diseases. By primarily focusing on the five organs, integrating the organs with their corresponding fu (bowel) organs, and supplementing with theories of meridians, qi, blood, and body fluids, most internal injury miscellaneous diseases can be appropriately classified. Furthermore, some diseases involve multiple organs and cannot be classified under a single organ; these are considered systemic diseases, such as deficiency syndromes and systemic lupus erythematosus.