Locus Minoris Resistentiae

LOCUS MINORIS RESISTENTIAE (Latin - place of lesser resistance), a figurative expression often used in medicine to explain the fact of a disease process affecting one organ or another. However, since questions regarding the mechanism of development of local processes, questions about the localization of diseases, remain to a large extent unclear even to the present time, the actual content that physicians invest in the said expression is by no means always sufficiently concrete. Clinical practice shows that even in the simplest cases, when it seems to be a matter of purely local diseases caused by some directly acting harmful agent (burn-gangrene, trauma-hemorrhage, fracture, etc.), the question of L. t. r. may have essential significance, since in this way it can be determined to what extent the resulting pathological effect should be attributed entirely to the said external factor: whether, for example, the given gangrene, and even the burn itself, are so significant because the site of the burn represents an L. t. r. due to loss of pain and temperature sensation (syringomyelia), whether there is also an L. t. r. in the form of fibrous osteitis, bone carcinoma, etc., at the site of traumatic fracture. The same approach to the question is especially indicated in those cases when a certain local suffering arises as if spontaneously, without obvious locally acting causes, or when such causes are present, the effect of their action, both in terms of its onset and in its nature, is unusual (trauma-tuberculosis, trauma-tumor). Finally, even in general diseases, for example infectious ones, local foci nevertheless arise in some quantity, signaling the presence of local prerequisites for the development of these foci.-When speaking of L. t. r., one has in mind parts of the body that vary considerably in extent: decreased resistance, resp. increased predisposition, may occur on the part of a microscopic tissue complex, on the part of some portion, for example a lobe of an organ, and finally of an entire organ; undoubtedly, entire systems may also figure as L. t. r. The conditions creating L. t. r. are very diverse. In a number of cases, the question is decided entirely in the plane of genotypic factors having a certain area of phenotypic manifestation; in this sense one can speak of L. m. r. in the spinal cord in Friedreich's ataxia; in the reticulo-endothelial system in Gaucher's disease, in the skin in ichthyosis, in the pancreas in diabetes, etc. In some cases, age is of essential significance: thus, this circumstance alone can explain the sharply expressed L. t. r. on the part of the digestive tract in children during various childhood infections (measles, scarlet fever, diphtheria, dysentery, gastroenteritis). The significance of the genotype should also be taken into account in seemingly purely paratypic diseases (tuberculosis, various forms of lead poisoning, etc.).-What anatomical, physiological, and biochemical prerequisites determine the predisposition of a particular organ or tissue to disease,-these questions remain to a large extent still unresolved. In any case, one cannot be satisfied here with general indications of biological incompleteness, rapid wear, of the so-called abiotrophy, etc. As more specific factors playing a role in the occurrence of L. t. r., the following can be indicated: 1. Anatomical factors. Here mention should be made of the degree, resp. perfection, of vascularization of various parts of the organ; this includes, for example, questions of the pathogenesis of osteomyelitis in childhood (in connection with the peculiarities of structure and vascularization of bones at this age); the predisposition to diseases of the uterus in the postpartum period may also be included here. Further, mention should be made of the significance of valve apparatuses subjected to mechanical influences; endocarditis is most often valvular rather than parietal; thrombosis of veins often also begins in the area of the valves. It is important to keep in mind the differences in the detailed structure of an organ, which may make some of its parts more vulnerable than others¹, for example the area of the lymphatic apparatus of the intestine, areas of mucous membranes lined with cylindrical epithelium, etc. 2. Pathophysiological, in particular mechanical factors, for example the degree of lateral pressure of blood, resp. the degree of resistance of arterial walls: the predominant development of atherosclerosis and syphilis of the aorta above the aortic valves, the connection between hypertension and arteriosclerosis, the development of the latter in the pulmonary artery system with prolonged and significant increase in blood pressure in it. It is well known that prolonged mechanical irritations in general create at their site L. t. r. to hyperplastic and neoplastic processes. L. m. r. can arise in the process of normal and pathological secretion of organs; thus, in a whole series of mucous membranes L. m. r. can be created ad hoc when these mucous membranes secrete various pathological products; for example, the excretion of heavy metals (bismuth, mercury), dysentery toxin, nitrogenous wastes by the large intestine often creates conditions for the development of diphtheritic inflammation of them, and this in turn can create L. t. r. for one or another secondary infection. Many nephroses, nephritis, hepatitis, gastritis, etc., can also be included here. Thus, entire organs and systems due to their inherent normal function of excretion can become L. t. r. in connection with the effect on these organs of excreted pathological products, including bacteria. In a number of cases one can speak of L. t. r. of purely professional origin; it is true that it is not always possible to establish the mechanisms that create in a given profession precisely this L. t. r. Thus, paralysis of the extensors of the hand in lead poisoning is usually associated with special tension of these muscles during work, the malignancy of the course of pulmonary tuberculosis--with certain types of pneumoconiosis. The question of professional cancers also belongs here, for example of the bladder in the aniline industry, of the face in the briquette industry, of lung cancer in some mining districts (Schneeberg, Johannisthal). Trauma is often the moment creating L. t. r. in relation to the most diverse sufferings not directly resulting from the trauma itself. Thus, at the site of trauma without damage to the coverings, abscess, tuberculosis of bones, possibly tumors (sarcomas, gliomas) may develop; trauma to the lung can lead to its inflammation. In a whole series of cases, post-traumatic (including postoperative) inflammatory processes in tissues arise in connection with the activation of the so-called dormant infection; in other cases, infection of the trauma area occurs hematogenously, revealing existing bacteremia in the subject: the blood pouring out during trauma already contains microorganisms which infect the damaged tissues, as L. t. r. Similar mechanisms creating L. t. r. can also be observed in physiological processes associated with hyperemia; it is precisely in this way that one has to explain the frequency of bone tuberculosis in children, tuberculosis of the sexual organs in the pubertal period, etc.: any hyperemia of an organ in the presence of bacteriemic factors is already a prerequisite creating L. m. r. in these organs.-Here one should also take into account biochemical factors, since on the basis of existing or created biochemical affinity of tissues (richness in cholesterol, lecithin, etc.) for one or another harmful agent (for example toxin, bacteria), the adsorption of the latter by the tissues increases.-Finally, local immunity in the sense of increased local tissue or organ sensitivity occupies not the last place in the problem of L. t. r. In general diseases, especially infectious ones, the occurrence of limited foci in various organs may owe their origin precisely to the prior sensitization of those places where such foci develop. It is known that such sensitization increases the ability of tissues to adsorb corresponding antigens, accelerates cellular and vascular reaction-in other words creates a number of necessary conditions for the development of a local process.--Thus, the occurrence of L. t. r. can proceed by the most diverse paths, and questions related to L. t. r. actually cover a significant part of the entire problem of pathogenesis (see). The connection with this problem becomes even closer if one takes into account the dependence of local processes (in the sense of their occurrence, course and outcome) on the general condition of the organism, on its general resistance, resp. predisposition. One should not think that L. t. r. indicates decreased resistance to all pathological processes; it is necessary to remember that L. t. r. in relation to one suffering can simultaneously become L. majoris resistentiae in relation to another (see Combinations of diseases). It is also completely natural that L. t. r. can turn into L. majoris resistentiae in relation to the same process-this will be local immunity.