TUBERCULOSIS. - An infectious disease that is usually chronic in its course but sometimes tumultuous and fulminating, caused by a particular bacillus (Mycobacterium tuberculosis) identified by R. Koch in 1882.
The disease has an almost ubiquitous spread and affects all ages, so much so that it is estimated that, excluding infants, 40-50% of cadavers show lesions from tuberculosis as a cause of either manifest or latent disease. Clinically, the disease is more frequent between the 2nd and 7th year of life, but mortality reaches its peak between the 14th and 30th year.
However, all ages can be affected, including old age, with lesions involving the most varied organs and systems, although by far the most frequent localization is in the lungs (70% in adults). The enormous spread of tuberculosis is also attested by some recent anatomopathological statistics by Naegeli (Zurich), according to which tuberculous lesions are found in 15% of cases in the first decade of life, 30-60% in the second decade, and as many as 99% in the last decades of life. According to Hamburger and Monti (Vienna), moreover, the tuberculin skin test (an indicator of manifest or latent, current or past tuberculous infection) would be positive in 99% of subjects by the 14th year of life.
Koch’s bacillus, a slightly curved rod-shaped organism, is characterized by a particular resistance to acids and common antiseptics, due to a resistant waxy capsule. This same capsule is probably also responsible for the limited efficacy of the various therapeutic measures currently known and for the long survival of the germ in the external environment. Today, three different types of tubercle bacilli have been identified: the human, the bovine, and the avian, but only the first two appear to be important in human pathology. Once these germs have entered the body, usually through the respiratory tract (96% of cases), or also through the digestive tract (1.4% of cases, mostly infants fed with milk from tuberculous cows), they produce characteristic tissue alterations with the formation of so-called tubercles or tuberculous granulomas, which constantly evolve toward a particular type of tissue necrosis, caseous necrosis.
Subsequently, depending on the virulence of the germ and the reactive capacity of the organism, the disease may follow a relatively benign course, with fibrous transformation and calcification of the tuberculous process (productive forms), or, conversely, there may be liquefaction of the preformed caseous material with ulceration and destruction of the host’s tissues and formation of cavities and fistulas (exudative and caseous forms). Naturally, this is not always a strictly schematic process, so that in clinical practice the two processes may coexist or alternate, which is why Michela more appropriately speaks of “predominantly productive forms” and “predominantly exudative forms.”
For a long time, tuberculosis was considered a hereditary and familial disease, but current views have changed considerably. Hereditary tuberculosis, in fact, linked to “genes” (preformed elements carrying hereditary traits, contained in the spermatozoon and ovum) and transmissible according to Mendelian laws, is today excluded by all authors. In very rare cases, one can speak of congenital tuberculosis, and this can only be admitted by demonstrating an ultra-virulent phase of Koch’s bacillus capable of crossing the placental barrier from mother to fetus, a phenomenon that has not otherwise been demonstrated. The only possible cases, therefore, are those determined by the passage of the germ through any placental lesions during pregnancy; hence the current general rule: one is not born with tuberculosis symptoms but becomes so. There is, however, no doubt about a particular hereditary predisposition to contract tuberculosis, as shown by statistics indicating that children are tuberculous in 43% of cases if both parents are affected, in 33.15% if only one is affected, and in 24.6% if the parents are healthy. Thus, rather than speaking of true hereditary transmission of the disease, one must speak of a hereditary predisposition linked to the particular constitution an individual has at birth and that makes him more susceptible to succumbing to tuberculous infection. It has been observed, in fact, that two particular biotypes (q.v.) provide the largest number of patients: the asthenic longilineal biotype (the phthisic or asthenic habitus of Stiller) and the lymphatic biotype with exudative diathesis (the pasty habitus of Czerny). While the former, however, due to the poor reactivity of its tissues, easily succumbs to the germ, presenting the most severe forms with ulcerative and necrotizing evolution, the lymphatic biotype, endowed with hyperactive connective tissue defenses, mostly presents chronic, circumscribed forms with fibrous evolution and thus relatively benign.
Alongside a predisposition to tuberculosis, one must also note the coexistence of a relative immunity to the disease, as evidenced by the fact that populations previously immune to tuberculous infection, once exposed to Koch’s bacillus, have shown a much higher mortality rate than populations where tuberculosis is considered an endemic disease. A case in point is the inhabitants of the island of Tahiti, who, upon accidental exposure to Koch’s bacillus through Portuguese colonization, suffered a tuberculosis mortality rate of 87.5% in a short time, reducing the population from 80,000 to 7,000 individuals.
These are, therefore, contrasting facts that are today explained by modern theories of allergy and immunity (q.V. MICROBIOLOGY), so much so that in the field of tuberculosis one speaks precisely of “tuberculous allergy,” in the sense of a deviated reaction from the normal. Ranke, who has studied this problem extensively, distinguishes three phases in the allergic process of an organism exposed to the tubercle bacillus. A first stage characterized by intense reaction of the affected tissue and formation of the “primary complex”; a second stage with a tendency toward generalization of the process due to hypersensitivity of the tissues to the harmful action of the germ; and a third stage, finally, characterized by a relative immunity and a tendency for lesions to localize in a single organ. This very simple schema may be excessive and cannot fully clarify the complex allergic problem of tuberculosis, yet it is of great help in explaining the differing responses, not only of individuals but of entire populations, to tuberculous infection. Among European populations, in fact, it is much more common for evidence of tuberculous infection to be positive from the earliest years of life, but on the other hand, continuous exposure to the germ and its toxins means that clinically the benign productive forms prevail due to the state of relative immunity.
From a clinical standpoint, tuberculosis can be distinguished as primary tuberculosis (characterized by the “primary complex,” usually localized in the lung) and post-primary tuberculosis, which, although it most commonly affects the lungs, can localize in any other organ or region (serous membranes, nervous system, peritoneal organs, bones, urogenital system, endocrine glands). The course of the various localizations is usually chronic; however, sometimes tuberculosis assumes a fulminant and rapidly fatal course, whether due to the extent of the process (miliary forms), the severity itself (galloping consumption or confluent caseous bronchopneumonia), the importance of the organ involved (tuberculous meningitis, adrenal tuberculosis), or the particular condition of the subject’s resistance (tuberculosis in infants, alcoholics). At other times, tuberculosis may run an entirely asymptomatic course and go unnoticed by the individual, yet such insidious forms are nonetheless of great medical and social importance, as they constitute a continuous source of contagion for the community. Tuberculosis is, in fact, of the utmost social significance, both for the damage it inflicts on the eugenics and demographic movement of a nation (some authors attribute to tuberculous intoxication of the fetus the capacity to induce states of psychodegeneration), and for the economic harm it can cause due to its characteristic chronicity, as well as for its contagiousness and high mortality, already noted above.
The struggle against tuberculosis is conducted first and foremost actively in a prophylactic sense. This prevention is now implemented everywhere directly by the State, or at least under its supervision, according to two directives: strengthening the organism so as to increase its resistance to infection, particularly during the age of development (establishment of colonies for predisposed individuals, supplementary rations, vaccinations, various hygienic measures); and reducing to a minimum the probability of contagion through the isolation of the sick (sanatoria, villages built specifically for this purpose, such as those at Papworth in England and Claire-Vivre in France) and the disinfection of environments.
In addition to the prophylactic field, notable progress has been made in recent decades in the therapeutic field. Current therapy aims primarily at three objectives: increasing the body’s defensive powers, combating the Koch bacillus, and circumscribing and reducing, even surgically, existing lesions in every way possible, so as to prevent the spread of the disease and promote the formation of a permanent scar. Important, therefore, have been the discoveries of certain drugs with bacteriostatic and bactericidal power against the Koch bacillus, such as “solone,” streptomycin, para-aminosalicylic acid, and isonicotinic acid hydrazide; these have made it possible to modify favorably the prognosis of certain forms of tuberculosis once considered invariably fatal, such as miliary tuberculosis and tuberculous meningitis. Less satisfactory results have been obtained with these drugs in cavitary pulmonary forms, in which any chemotherapeutic therapy must be combined with collapse therapy. This therapy, initiated by Forlanini, is based essentially on the principle of resting the diseased part of the lung so as to allow easy cicatrization of the tuberculous lesion. The essential method is therefore pneumothorax (pnx), by which air is introduced into the pleural cavity in such quantity as to neutralize the negative pressure normally present there. Over time, this method has been continually refined and has undergone modifications, so that today not only are hypertensive and hypotensive pneumothoraces distinguished, as well as homolateral and contralateral, and bilateral, but an extrapleural pneumothorax is also performed when the presence of excessive adhesions between the parietal and visceral pleura prevents the introduction of air into the pleural cavity. There are, moreover, today numerous other methods of collapse therapy that fall within the province of surgery, though not devoid of beneficial effect in certain circumstances (pleurolisis, intrapleural pneumothorax, phrenicectomy, partial or total resection of the diseased lung, etc.). According to most modern authors, tuberculous therapy must always be based, in pulmonary forms, on collapse therapy, but the beneficial effect of antituberculous drugs cannot be denied, especially from the social standpoint, given their capacity to render tuberculous patients non-contagious—patients who, as is known, transmit the disease in the environment through the microscopic droplets of saliva projected by coughing and containing Koch bacilli.
A final note must be made regarding the medico-moral problems connected with tuberculosis. These concern particularly the burial of the deceased, the imposition of an examination to determine the presence or absence of the disease, marriage, and pregnancy. In all these cases, the inevitable clash is evident between coercive legislation, which places the interests of the community first, and the rights of the individual. Finally, it must be recalled that until a few years ago, tuberculosis was one of the most frequent indications for therapeutic abortion (v.). At present, however, the majority of phthisiologists and gynecologists hold that, while in some severe forms pregnancy may be advisable to avoid, therapeutic abortion is to be proscribed because of the serious harm inevitably entailed by the interruption of pregnancy; all the more so since in the most severe forms spontaneous abortion often occurs, which is less traumatic and dangerous than induced abortion.