Morbid Anatomy
It has been truthfully affirmed that we know more of the results or products of gout, and less of its essential nature, than of almost any other disease. Thus the post-mortem history of the disorder is concerned almost exclusively with more or less graphic accounts of the uratic deposits, their sites of predilection, and the changes that they induce. Hence it is that the morbid anatomy of gout relates for the most part to its regular or articular manifestations, for it is in and around the joint structures that the deposits for the main part occur.
As to the assumed localisations of the disease in the internal organs, there is no anatomical evidence that they are due to an invasion of the “gouty” inflammation. Not even the renal changes, despite the attestation, as it were, of the gouty process by uratic deposits in the papillæ, can be held as distinctive of gout. Norman Moore found them present in only twelve out of eighty cases. As Osler said, “The presence of uratic concretions at the apices of the pyramids is not a positive indication of gout. They are not infrequent in this country [U.S.], in which gout is rare.... It is not possible to say in a given case that the condition has been due to gout unless marked evidence of the disease co-exists.”
If, then, nothing distinctive can be claimed of the renal, how much less can we construe as “gouty” the anatomical alterations that may or may not be met with in other organs in this disorder. In short, it may be said of the renal as well as the other visceral lesions, so often met with in association with gout, that they are met with even more frequently in its absence, and most certainly fail to attest their “gouty” nature by the appearances which they present.
The only morbid structural changes, therefore, that can legitimately be defined as specific of gout relate to its regular or articular lesions. As to the anatomical alterations in the articulations, their specificity depends essentially on the uratic deposits, rather than upon the associated inflammatory and degenerative processes.
Given death during an acute paroxysm, examination reveals the usual tokens of inflammation, hyperæmia, effusion, and swelling of the ligamentous tissues. The synovial lining is injected and spongy, while the exuded fluid is thick, scanty and turbid, containing polymorphonuclear leucocytes as well as crystalline deposits. Charged therewith, not only is the synovia thick, but of a milky appearance. Examined microscopically, it is found to contain the acicular crystals of sodium biurate. The synovia has occasionally been found covered with blood, but no pus formation has ever been known to occur in uncomplicated acute gouty arthritis. The reaction of the synovial fluid is generally neutral or alkaline, but exceptionally Garrod found it acid.
Uratic deposit has a predilection for cartilage, and in some instances is strictly confined thereto; but in the more chronic forms it permeates all the component elements of the articulation. In the synovial membrane and fringes deposition takes place in the subepithelial and subserous layers. It invades also the ligaments, the tendons, and even the periarticular fibrous tissues become impregnated with biurate. Moreover, like the synovial sheaths of the tendons, the neighbouring bursæ are specially prone to deposits, which again encroaching upon the subcutaneous connective tissues, infiltrate the skin itself, forming chalk stones or tophi.
Inspected after death, the articular cartilages are seemingly overlaid with a white mortar or chalk-like material, i.e., sodium biurate. Their surfaces, however, though defaced by stains, streaks, or dull patches, nevertheless, at any rate at first, retain their pristine smoothness. This because closer scrutiny reveals that the deposit is not in reality upon the surface of the cartilage, but is located interstitially in its substance.
Microscopic examination of a vertical section, taken at the site of the deposit, shows clearly that it is composed of felted masses of acicular crystals. Lying in the matrix of the cartilage, they are more densely packed just below its free surface. The crystals do not penetrate further than one-third or one-half of the depth of the cartilage. Becoming more and more sparse towards the deeper layers, those near the bone are entirely free from deposit. This clearly indicates that the uratic matter originated from the synovial fluid bathing the articular ends and was precipitated therefrom.
As to the primary site of the deposition, it usually takes place at the centre of the articular cartilage. Opinions differ as to whether the cartilage cells are foci of deposition. Garrod thought so, but Duckworth found no relationship between it and any histological elements, while others locate it in the matrix.
While, as before stated, the cartilage at first retains its smoothness, later it becomes pitted in patches. Ultimately the cartilage, through atrophic changes and erosions, may disappear, the joint cavity becomes filled with a plaster-like material, and the joint structures undergo more or less disorganisation. Pari passu with the central atrophy of the cartilage, hypertrophic outgrowths form at its free margin. In late stages the bones, too, undergo changes; their outer layers become more dense through proliferative osteitis, while their spongy tissue becomes rarefied, and the cells of the marrow fatty. Duckworth held that uratic deposits might occur primarily in the bone without any similar implication of the related cartilage. On the other hand, Garrod dissented, claiming that when the bone was involved, it was only secondarily to uratic deposition in the cartilage, of which indeed it was but an extension.
In reviewing the foregoing findings, it must be admitted that morbid anatomy fails to shed light on the essential cause of gout. This, at any rate, is true of the older studies with which, up to the present, we have been engaged. Still, as Berkart’s more recent researches show, our knowledge of even the morbid anatomy of gout is as yet but in its infancy.
Histological examination of the articular ends adjacent to gouty joints reveals the presence of certain cystic changes in the diaphyses. Thereupon Berkart propounded an hypothesis, explanatory of the acute phenomena of a paroxysm of gout. His view was that these cysts in the bone, at first minute, gradually enlarge. Ultimately, through concomitant thinning of the surface bone, there comes a day when the cyst bursts into the joint, its content voided into the cavity thereof.
An interesting point noted by Berkart was that in many cases of “acute” gout the articular cartilage was found apparently normal and devoid of uratic deposits, and this although the attack had been sufficiently severe. This would appear to contravene Garrod’s dictum that “gouty inflammation is invariably attended with deposition of urate of soda.” The same inference was drawn from a case of Sir Dyce Duckworth’s. The subject had had two attacks of gout in the right great toe joint. Yet at the autopsy neither toe joint contained a speck of uratic deposit. Nevertheless, this does not prove that uratic deposition had not ensued during the gouty attacks. All it can be held to prove is, that such deposits are not always permanent, and that, under certain conditions, they may undergo resolution. That this is so is almost certain, seeing that tophi in the ear have been seen to come and go, and equally certainly, after an acute attack, tophi in the neighbourhood of a joint may lessen even though fresh ones form coincidently at another site.
Albeit, the importance of Berkart’s hypothesis and histological findings resides in the fact that they suggest strongly that a pathological process, more vital and biological than the mechanical uric acid theory, is at the root of the clinical phenomena of a gouty paroxysm. It does not put out of court Garrod’s assumption that uric acid is an invariable accompaniment of acute gouty inflammation, but it militates strongly against his contention that uric acid deposition is the cause of acute gouty inflammation. It indicates the reverse, viz., that the uratic deposition is the consequence of a more vital underlying morbid process.
Let us revert now more in detail to Berkart’s findings. The bones adjacent to gouty joints were fully prepared for microscopic examination. Investigation of the first metatarsals, and in some instances of the phalanges also, revealed the presence of cystoid degeneration. Its starting point is in the epiphyses. Thence it extends to the articular cartilage, through which it bores at one or more points. The contents of the cyst then find their way into the joint through the fistulous openings in the cartilage, with a resultant acute “perforative synovitis.”
The cysts, at first minute, may be either single or multiple. Small in size, they are easily concealed by the fat marrow, unless the bone is properly prepared for microscopic examination. The isolated cysts eventually coalesce, and so lead to considerable excavation.
As to the contents of the cysts little is known, as, save through accidents or surgical operations, they are rarely available for examination. When of relatively recent origin they apparently consist of a coagulable substance which later on become serous or hæmorrhagic. So long as the fistulæ thus formed in the cartilage remain pervious, a direct way into the articular cavity is provided, and through this, if of sufficient calibre, the necrotic matter periodically gains entry into the joint, with ensuing periodic outbreaks of acute synovitis. In other instances in which the cysts are located in proximity to, or within, the diaphysis they may fail to extend to the cartilage, and no perforation ensues. In this event, through accumulation of its contents, the cyst enlarges, and the bone is gradually expanded through pressure.
Berkart holds that the histological changes in the affected epiphyses indicate that the cystoid degeneration is the outcome of an anomaly of the vascular and osseous structures. The degenerative area contains an abundance of dilated and thin-walled veins, evidence of a condition of chronic congestion. In consequence thereof, the trabeculæ undergo decalcification, and the adjacent fat marrow becomes fibrous. The areas of fibrosis thus formed, owing to thrombosis of the related veins, become softened and transmuted into cysts.
Now, as we all know, some persons, after indulging in wine, almost immediately experience sharp twinges in the small bones of their hands or feet. Garrod attached diagnostic importance to such swift response as a sign of gout. These pains he attributed to uric acid deposition. In contrast, Berkart attributes the twinges to atony and consequent over-distension of the related vessels, which lack the normal support afforded by the osseous trabeculæ.
As far as we are aware, these findings of Berkart’s are as yet unconfirmed. Nevertheless they provide us with a much more probable explanation of the phenomena of acute gout than the older uric acid theory, which, not to mention the many other obstacles to its acceptance, has always laboured under the aspersion of being too “mechanical” in conception.
Moreover, his studies clearly indicate that not only the intra-articular surfaces but the adjacent bone-ends and marrow must, as the somewhat rare opportunities present themselves, be exhaustively investigated. For myself, I cannot believe that so passive an agent as an “anomaly of the vascular and osseous systems” is the fons et origo mali in gout. Some more vital element must, I feel convinced, intrude, and I incline to think an infection. Berkart himself brings forth evidence in favour of this contention, inasmuch as he noted the frequent co-existence of lymphangitis, so pronounced that the whole of the affected leg became the seat of a leuco-phlegmatic œdema.
CHAPTER V
PATHOLOGY OF GOUT—PROTEIN METABOLISM
Not only is the proximate cause of gout unknown, but the essential nature of the disease is still shrouded in obscurity; for the obliquity in trend of protein metabolism, manifested though it be by striking phenomena, is clearly only the outcome of some, as yet undetermined, derangement in the mechanism of intermediary metabolic or bio-chemical change.
This is, of course, but to restate the problem we are confronted with. Wholly to solve the enigma would postulate ability on our part to trace ingested foodstuffs through all their vicissitudes from the moment of entry into the blood or lymph-stream till flung out as effete matter through the various avenues of excretion; but, unhappily, we know the story only in part, its beginning and end, but not what lies between.
We know much of the complex changes that take place in food prior to absorption, and of the modus operandi of the latter not a little. Comparably, too, we can gauge the quality and quantity of end-products, the chemical outcasts, as they escape in the urine, sweat or breath, and largely how achieved; but of the intermediate steps between absorption and excretion we catch but a glimpse here and there. The sequestered path by which the inanimate molecules of food uprise to Life, and anon go down to decay and death, are still hidden.
In other words, little do we know of the relationship of labile, or food-protein, to tissue protein. True, the coarse fact of abnormal protein loss in renal disease may be revealed in the urine, as likewise the waste of albumoses in myeloma, etc., and the incidence of amino-acids in disease of the liver. Similarly, the appearance of cystin or of alkapton in the urine bespeaks flaws in protein metabolism, failures in the normal disruption of amino-acids. All these are of the grosser anomalies of protein metabolism, but more subtle those of gout!
Complex, in truth, the problem here presented, than which none more subtle exists in the realm of bio-chemistry. True, quantitative variations in the content of the urine as to urea, uric acid, etc., undoubtedly bear a direct relation to protein metabolism, but they give us little, if any, substantial clue as to the particular metabolic warp responsible. We see this particularly in regard to uric acid, so long accredited with an essential rôle in gout.
Thus we cannot, on the basis of the variations in its excretion only, presume to diagnose “gout.” This because even more extensive variations occur in healthy persons. On the other hand, attacks of gout never occur when urates are absent from the blood. To reduce the amount of these urates is clearly then of importance, and obviously to this end a knowledge of their source is essential. We have an analogy to hand in diabetes, in which the somewhat similar problem relating to glycosuria has been partially solved.