PATHOLOGY AND CLASSIFICATION.—The lesions of pulmonary syphilis may be divided into four classes: (a) early phthisis, associated with principal interlobular proliferation; (b) advanced syphilis, in which gummatous or allied formation exists; (c) simple phthisis, developing in consequence of impaired general health induced by syphilis; (d) inherited or congenital syphilis, occurring in infants.
(a) The pathological process in the majority of cases in the adult is interstitial new formation, very often evoked by antecedent catarrhal inflammation. At first small spindle-shaped and round cells appear and develop into connective tissue, among the fibres of which blood-vessels are freely produced; the septa of the alveoli are thickened and the alveoli themselves compressed. In any morbid process in the lungs, such as tubercle, sarcoma, or cancer, the alveoli act as the inter-fascicular spaces of the connective tissue. In the same manner in syphilis the alveoli of the lungs are always in the later stages, and sometimes primarily, more or less filled with small cells, which, surrounded by the newly-formed connective-tissue fibrous framework, gives the appearance of some of the forms of simple phthisis. The smaller bronchi become narrowed, and perhaps occluded, by the pressure of the new growth which develops along their lumen. Occlusion of the bronchi may also be caused by enlargement of the bronchial glands, which is one of the incidents of the syphilitic pulmonary process.
If we endeavor to nucleate the peculiar impress attributed to early syphilitic pulmonary processes, we find much that is vague. The vascularity and advanced grade of organization of the new growth are considered by Greenfield and Goodhart to be characteristic when compared with tubercular consumption, in which the original growth is bloodless and the tendency is to retrograde metamorphosis. Green and Virchow suggest that the origin of syphilitic diseases of the lungs is distinctive in this respect, that while in the ordinary forms of phthisis the fibroid is secondary or coequal in its development with changes in the alveoli and alveolar wall, in syphilis there are primarily interstitial changes. In chronic bronchitis the fibroid thickening proceeds from the bronchi. Wagner, however, maintains that implication of the alveolar wall is as common in syphilis as in ordinary phthisis.
In the general pathology of syphilis the change in the intima of the blood-vessels is characteristic: this has not yet been demonstrated in the lung, but merely the general thickening of the external coat of the vessels. When entire vesicular consolidation and breaking down occurs, the process is similar to ordinary phthisis, and indistinguishable from it.
(b) In the gummatous stage the same formation of cellular and connective tissue is found as in the diffused form, with which gummata are often associated. Gummata may originate anywhere in the intervesicular tissue, usually near the visceral pleura. Sometimes they are formed near the roots of the lungs, intimately connected with the blood-vessels and bronchial sheaths. They may also be formed in the deeper layers of the costal pleura or upon the periosteum of the ribs. Owing to the peculiar anatomical formation of gummata, their subsequent history is one of combined caseous and fatty degeneration. These centres of softening may communicate with a bronchus, more or less rapid evacuation of the mass may occur, and a cavity be formed which often enlarges as the gummata break down. Contraction may ensue, leaving a small fibrous scar with cheesy cretaceous deposit, or the gummata may point externally, with or without the appearance of inflammation in the adjacent tissues, or they may remain stationary for an indefinite period. In some cases the pulmonary new formation may be a combined interstitial, gummatous, and catarrhal process; but, as a rule, the fibroid process of syphilis in the earlier stages is not accompanied by the filling of the alveoli with catarrhal cells. Gummata developed in or near the pleural sac may increase in size, and by compressing the lung simulate pleural effusions.
(c) The morbid anatomy of cases in which simple phthisis develops in consequence of the vulnerability of the pulmonary tissues to the exciting causes of bronchial inflammation requires no special consideration.
(d) Interstitial inflammation, gummata, and enlargement of the bronchial glands have been found in the syphilitic foetus and in very young children. It is also claimed that syphilitic disease of the lung may be one of the forms of tertiary disease which develop in children between the second dentition and maturity. Virchow and Lebert have described pulmonary gummata in children suffering from inherited syphilis. Depaul gives the cases of two children with pemphigus who had soft puriform nodules or collections scattered through the lungs. In the infant lung the highly cellular character and ready reversion to the embryonic type of structure would naturally lead to exuberant growth and rapid diffusion of the morbid process, which could not occur in the more fibrous, less cellular lung of the adult. Hence the slower growth in the latter establishes the more fibrous and limited extent of disease: in other respects the origin and distribution of the growth are identical in both cases. In the infant enlargement of the bronchial glands and bronchitis leading to broncho-pneumonia, or an unusual proliferation of epithelium in the alveoli, is more frequent than in the adult.
MORBID ANATOMY.—In the earlier stages of pulmonary syphilis the macroscopic appearance of the lung is firmer at the seat of deposit than elsewhere. It is also heavier and has a smoother surface. The infiltrated parts are grayish-red or grayish-yellow, smooth, and homogeneous. Sometimes the appearance resembles pale-whitish patches invading districts of the lung. The hyperplastic material becomes converted into a tough, contracting, fibrous tissue, which radiates through the lung, drawing together the bronchial tubes and flattening them, possibly even to obliteration. The entire lung may be involved, but the changes most frequently proceed from the hilus of the organ into the interior, following the track of the bronchial radicles and the bronchial and pulmonary arteries. The lesions frequently develop near the visceral pleura, where there is more connective tissue. This accounts for the depressed puckered scars which are found on the pleural surface.
The macroscopic appearances in specific pulmonary disease differ, according to Goodhart, "both from a chronic pneumonia and from that solidification ensuing after contraction of the lung from old pleurisy, in that it is less evenly distributed, and generally less widely spread over the lobe, than they. It is nodular, rather diffused, and more symmetrical than unilateral. From miners' phthisis the appearance differs in the absence of the extreme dilatation of the bronchial tubes and more solidity from greater growth. The tissues involved are more tough and less granular than red or gray hepatization." It is possible to differentiate other forms of fibroid phthisis by noting, in addition to the above points, the presence of the syphilitic process in other viscera, and by comparing the clinical records with the post-mortem examination.
Syphilitic lesions may be found in any part of one or both lungs, but their localization at definite points in the lungs, leaving the balance free even when the lesion has proceeded to formation of cavities, may be characteristic. There is, however, a wide division of professional opinion upon the subject of the localization of the process in syphilitic pulmonary disease; some claiming the middle lobe, some a symmetrical lesion at the apices, others lesions at a definite point elsewhere than at the apices. If the pulmonary lesions are introduced by an attack of pleurisy, the process in the lungs is usually located at one or both bases. Some, however, locate the disease at the base, without mentioning an antecedent pleurisy.