The dermis can be divided into the papillary dermis, which is the thin zone immediately beneath the epidermis and, lying deeper, the thicker reticular dermis. Vital to the dermis are the fibroblasts which have spindle-shaped cell bodies and nuclei. They produce the fibres which can be recognised in the dermis by light microscopy. Collagen is by far the most abundant constituent of these filamentous components of the dermis.
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Figure 6-1: Nodular configuration and extension into dermis (haematoxylin & eosin). a dermis; b sweat gland and duct; c normal fascia; d cellular fibrous tissue |
They described changes in the palmar fascia as well as in the adjacent tissues and observed that "the characteristic change is the proliferation of fibroblasts in the nodules of the contractures". They were the first investigators to attempt a functional interpretation of the histopathological changes observed in Dupuytren's disease by assuming that the cellularity of the nodules was indicative of the activity of the disease. They suggested a gradation in four stages to reflect the activity of the proliferative process. With regard to the surrounding connective tissues changes, they noted that in advanced cases of Dupuytren's disease "evidence of subcutaneous adipose tissue is not revealed and sweat glands are rare or completely absent". This was the result of an increase in the size and number of connective tissue bands which normally separated the lobules of fat. There was also an increase in the number of capillaries in the interstitial connective tissue and the capillaries were infiltrated by lymphocytes.
Luck (1959) classified the disease into three stages: proliferative, involutional and residual. He defined the nodule, focus of proliferating fibroblasts, as the initial lesion in the proliferative stage. He wrote: "in this local fibroplasia, the fibroblasts do not align themselves with lines of stress and have, in fact, no purposeful arrangement" (fig. 2, 3, 4).
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Figure 6-2: Varying cell density within an active lesion (haematoxylin & eosin). The fibroblasts do not align themselves. a cellular and dark staining area; b less cellular but still abnormal area |
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Figure 6-3: cf. figure 2 |
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Figure 6-4: Non-oriented cells with large nuclei. They are typical of active fibroblasts. a mitosis |
The involutional stage was characterised by fibroblasts aligning themselves with major lines of stress that pass through the nodules (fig. 5). Luck considered that the fibrous cords represented reactive functional hypertrophy, in response to the repeated tension stresses on the hand, of fascia from which the nodule took its origin, hence the term reactive tissue. Finally, with the complete involution of the nodule came the residual stage which he described as follows: "the nodule disappears leaving only a focus of dense adhesions and the reactive proximal fibrous cord which is almost acellular and tendon-like".
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Figure 6-5: Involutional stage. a fibroblasts aligning themselves with the lines of stress |
Further histological studies have shown that Dupuytren's disease can be classified into several stages according to their cellularity, that these different stages can coexist in the same specimen and that different cell populations predominate in each phase (Mohr et al., 1993). Nezelof (1985, 1986) distinguished two evolutionary stages and Shum (1990) three (table 1). In general, the cellularity in the nodules is high whereas the fascial bands, made up of densely packed collagen fibres, are relatively acellular (Nezelof, 1985; 1986).
| Early lesions | Focal increase in vascularity with ingrowth of capillariesand proliferation of endothelial cells |
| Proliferation of perivascular cells, many of which are desmin positive and probably akin to perivascular smooth muscle cells | |
| Formation of angiocentric, nodular lesion by centrifugal spread of proliferating cells | |
| Extravasation of red cells focally from the newly formed capillaries | |
| Production of reticulum but not elastic fibres | |
| Intermediate lesions | Proliferating cells are undergoing morphosis from cells with round nuclei and scanty cytoplasm to spindle-shaped cells with indented, elongated nuclei and a moderate amount of cytoplasm (features of myofibroblasts) |
| Lesion becomes less cellular with increasing stromal collagen | |
| Alignment of cells among lines of stress | |
| Fibrous infiltration of adjacent skin and subcutaneous tissue | |
| Focal deposition of haemosiderin pigment as a result of degeneration of extravasated red cells | |
| Lymphocytic infiltration | |
| Late lesions | Relatively acellular cords |
| Densely packed and aligned collagen fibres | |
| Cells appear as fibrocytes, few are positive for desmin |
The fibroblasts could thus be responsible of the retraction. The observations published by Gabbiani and Majno in 1972 showing the presence of myofibroblasts in Dupuytren's disease, ultrastructurally similar to myofibroblasts of granulation tissue where they were thought to be responsible of wound contracture, gave likely explanations for the retraction mechanisms.
Myofibroblasts are connected to the extracellular matrix by fibronexus, which are transmembrane complexes of intracellular microfilaments in apparent continuity with extracellular fibres. Fibronexus are probably the element through which the forces generated by the actin filament bundles of myofibroblasts are transmitted to the extracellular matrix (Singer et al., 1984) and the gap junctions found between these cells may synchronize their contractile action.
The in vitro contraction of myofibroblast-containing tissues in response to various drugs known to act on smooth muscle contraction strongly suggests that myofibroblasts are responsible for the contractile events of wound healing.
One can, by using biologic markers, show the presence in the cytoplasm of myofibroblasts of vimentin (V) from fibroblastic origin and of alpha-actin (A) and desmin (D) from smooth muscle origin (Mohr & Wessinghage, 1993). It is likely that the myofibroblasts are responsible for the synthesis of type III collagen (Gabbiani and Montandon 1986).
The cellular derivation of myofibroblasts is a subject of discussion. A fibroblastic origin seems probable in granulation tissue whereas a smooth muscle origin has been proposed for the myofibroblasts found in intimal thickening of atherosclerotic vessels. The presence of desmin in the myofibroblasts found in Dupuytren's nodules speaks for a smooth muscle origin (Shum et al., 1988).
Using the markers of the cytoskeletal proteins, it is possible to define phenotypes among myofibroblasts (Schürch et al., 1990; Gabbiani, 1993):
These phenotypes allow the distinction of two types of myofibroblastic proliferations. The first contains only V cells and is found in normally healing granulation tissues, eschars and normally healed scars. The second is found in hypertrophic scars, in fibromatoses and Dupuytren's disease. In this type, the V cells are mixed with various proportions of cells expressing cytoskeletal markers of myogenic differentiation, i.e. VAD-, VA- and VD-cells. In most Dupuytren's nodules and other fibromatoses the number of VA-cells exceeds the number of VAD-cells. The tissue distribution of VA- and VAD-cells is homogeneous in some cases but in others it is local. It is unknown whether these differences in the regional distribution of cells with various phenotypes affect the course of Dupuytren's disease.
This heterogeneous cytoskeletal composition of myofibroblasts raises new questions as to their origin. Ultrastructural data provide evidence that during pathological and/or culture conditions fibroblasts and smooth muscle cells acquire morphological features similar to those of myofibroblasts (Schürch et al.,1990) thereby suggesting that both cell types may be the progenitor of myofibroblasts. The heterogeneous cytoskeletal composition of myofibroblasts seems to be in agreement with that theory since V-cells could be derived from fibroblasts, and VAD- and VA-cells could be derived from smooth muscle cells and/or pericytes.
A vascular origin of myofibroblasts in Dupuytren's disease has also been proposed on the basis of morphological observations, suggesting that desmin-positive cells were migrating from vessel walls to the tissue (Shum et al., 1988). Autoradiographic investigations (Mohr et al., 1993) on specimens of Dupuytren's disease have shown that proliferative cells are preferentially present in vascular or perivascular areas in accordance with the findings of Kisher et al. (1984) and Murell et al. (1989) who suggest that "the crucial phenomenon of fibroblast proliferation begins around narrowed microvessels". This observation has led Murrell et al. (1993b) to study the role of localized ischemia and of oxygen free radicals in the development of Dupuytren's disease
Perivascular connective tissue may contain a peculiar type of cell that has been termed pericyte. The assumption that pericytes may be involved in the pathogenesis of Dupuytren's disease is supported by the immunohistochemical investigations of Andrew et al. (1990, 1991) who found that pericyte proliferation was present around occluded capillaries in the fibromatous foci. The expression of smooth muscle alpha-actin in pericytes and myofibroblasts further supports this finding.
It must however be noted that the uniqueness of Dupuytren's contracture myofibroblasts has been contradicted by Murell et al. (1991, 1993a) who were able to show that the presence of myofibroblasts in the palmar aponeurosis is not specific to Dupuytren's disease. By comparing specimens of palmar aponeurosis in patients operated for Dupuytren's disease or for a carpal tunnel syndrome, they showed that all fibroblasts in the palmar aponeurosis (with or without a Dupuytren's disease) show ultra-structural features of myofibroblasts. By contrast, the fibroblast density was sixfold to 40-fold greater in cords and nodules from Dupuytren's contracture than in carpal tunnel syndrome.
McCann et al (1993) were able to demonstrate that the proliferation of myofibroblasts in patients with Dupuytren's contracture goes well beyond the limits of the fascia to reach the dermis and even, in some cases, the epidermis. This could explain the high recurrence rate after simple fasciectomies.
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Figure 6-6: Folding of the collagen fibres. The distance between origin and insertion of the palmar fascia is decreased but the overall length remains the same (from Glimcher and Peabody 1990) |
One could conceive that the longitudinal shortening of the aponeurosis is due to some kind of pleating and folding of the collagen fibres as suggested in figure 6. This hypothesis cannot be confirmed because X-ray diffraction studies of palmar fascia in Dupuytren's disease patients fail to show any evidence that the collagen is reordered and redirected (Brinckley-Parsons et al., 1981). Furthermore, electron microscopy studies made by Legge et al (1981) have shown a normal helicoidal structure of the collagen incompatible with the folding hypothesis.
Another hypothesis would be that the collagen fibres are shortened by a chemical denaturation and an alteration of their tridimensional structure. This hypothesis must be eliminated for the same reasons as the preceding one.
The only explanation then, is that the overall longitudinal length of the palmar fascia is shortened because some of the palmar fascial tissue has been removed. This is accomplished by the resorption of some of the palmar fascial tissue and its replacement by newly synthesized collagen while the origin and insertion of the tissue are moved closer together by some external force (fig. 7). That external force would be produced by the myofibroblasts. This explanation is compatible with the observations that show an increase in the resorption of type I collagen and in the production of type III collagen.
Another observation about the relationship between collagen and myofibroblasts is of great clinical significance. One was able to show (Glimcher et al., 1990) that fascia deliberately taken by the surgeon at the farthest distance from clearly involved Dupuytren's tissue and representing specimens indistinguishable clinically and histologically from normal palmar fascia, in all cases showed all the biochemical changes seen in Dupuytren's collagen. Even at the ultrastructural level, there was no discernible pathology in the collagen or in the morphology of the cells. The chemical changes were present whether or not myofibroblasts were visible and they occur before the fibroblasts are morphologically modified or replaced by myofibroblasts. This clearly demonstrates that it is unthinkable to surgically remove all the fascia involved by Dupuytren's disease.
Even in the presence of well-developed myofibroblasts, knuckle pads do not retract. This could indicate that the contracture is not the result of cellular events but might depend on external factors such as the anatomical site and functional activity of that particular area.
Growth factors are signal polypeptides that are intimately involved in the control of cell growth and differentiation. Like classic peptide hormones, they bind to specific receptor proteins on the surface of target cells and regulate a variety of cellular functions through the activation of intracellular signals. Several studies (Badalamente et al., 1992; Lappi et al., 1992; Alioto et al. 1994) have implicated various growth factors in the Dupuytren's disease process.
Three growth factors were shown to have effects on fibroblasts in vitro. Specifically, bFGF and PDGF proved to be primarily mitogens for cells cultured from both normal fascia and Dupuytren's fascia while TGF-beta was a potent stimulator of collagen and noncollagen protein synthesis. Yet qualitative and quantitative differences were demonstrated in the response to the growth factors between normal fascia fibroblasts and Dupuytren fibroblasts. This implies some variation in receptor type, receptor number or a combination of both. This variation could be genetically determined.
Lappi et al. (1992) have proposed a model of the pathophysiology of Dupuytren's contracture based on the potential contribution of growth factors. They suggest that the palmar fascia will be exposed to repeated microhemorrhages due to ischemic vascular disease, liver pathology, trauma or other causes. Because of their genetic predisposition, these normal palmar fascia fibroblasts will respond abnormally to the enduing release of platelets and inflammatory cells. Cells in the fascia are now exposed to PDGF and TGF-beta, both known to be released in high quantities from platelets. PDGF stimulates fibroblasts proliferation and exposure to TGF-beta initiates the production of collagen. In patients who develop Dupuytren's contracture, the genetically altered fibroblasts ate more sensitive to these growth factors. The fibroblasts proliferate and produce abundant collagen. As this proliferation continues unchecked, the thickened fascia eventually becomes hypovascular and more prone to hypoxia and microhemorrhages. The production of oxygen-free radicals stimulates further proliferation of abnormal fibroblasts. A vicious cycle ensues.
This schema incorporates what is known about Dupuytren's contracture etiologically, histologically and biochemically. It suggests many possible ways to link the treatment of Dupuytren's disease with its known pathophysiology.
These observations are clinically important and have practical consequences: