Cerebriform plantar hyperplasia: ultrastructural study of two cases

ARTICLE

The Proteus syndrome is a complex congenital hamartomatous disorder where certain connective abnormalities are characteristic. The major clinical findings as proposed by Wiedemann et al. [1] and further delineated by other authors [2-4] are: gigantism of the hands and/or feet, systematized epidermal nevus, partial or complete hemihypertrophy, subcutaneous tumors (lipomas, limphangiomas, hemangiomas, connective tissue nevus), skull anomalies, accelerated growth and visceral abnormalities.

Typical cerebriform masses of the soles, a distinctive feature of this disorder, has been described as cerebriform plantar hyperplasia (CPH) [3-6].

The purpose of this work is to give a description of the structural changes seen in the CPH, in order to establish histopathological patterns that may help in the diagnosis of this lesion which we consider pathognomonic of the Proteus syndrome.

In this work we report the results of light and electron microscopy studies of the plantar tissue from two previously reported cases [7] with a mild form of the Proteus syndrome, presenting unilateral macrodactyly and an irregular thickening of the plantar surface.

Materials and methods

Skin biopsies from the plantar tissue of two children affected with cerebriform plantar hyperplasia were surgically excised. As a control, a sample was taken from normal plantar tissue of the non-affected foot of one of the patients.

Samples were fixed in 10% formaldehyde solution and embedded in paraffin for light microscopy studies. Sections were stained with hematoxilyn-eosin as a routine technique and with Verhoeff-van Gieson for elastic fibril demonstration.

For electron microscopy, similar samples were fixed in 4% glutaraldehyde in 0.1 M phosphate buffer pH 7.4; post-fixed in 1% osmium tetroxide; dehydrated in a graded ethanol series followed by acetone and embedded in Spurr resin. Ultrathin sections were stained with uranyl acetate and lead citrate and examined under an EM Zeiss 109 transmission electron microscope.

Results

Light microscopy

Conspicuous differences between the involved plantar skin and the control normal skin could be observed. In both pathological samples the most notable changes were the increase of the fibro-adipose tissue and of the adnexal structures in the dermis. The reticular dermis exhibited distorted collagen bundles of different thickness and orientation. The elastic van-Gieson stain showed few and fragmented elastic fibrils. Hypertrophic and hyperplastic adipose tissue was present subcutaneously among collagen bundles. Amidst the adipocytes, an increased number of eccrine sweat glands as well as peripheral nerve structures were also present in the deep dermis (Fig. 1).

Electron microscopy

In the uninvolved control skin the dermis was occupied by collagen fibers with regular periodicity. They formed regular sized bundles running in a defined direction. Fine filamentous structures corresponding to tropocollagen fibrils were seen close to the fibroblasts. Elastic fibers of normal morphology were seen between the collagen bundles. Normal oval-shaped fibroblasts scattered throughout the dermis could be seen.

The involved plantar tissue showed a diminished number of shape-altered fibroblasts with pyknotic nuclei and scant cytoplasms (Fig. 2). In general, their intracytoplasmic organelles were reduced in number. Densely packed collagen fibers arranged in bundles of variable configuration and orientation were observed (Fig. 3). In cross sections the fibrils exhibited either normal or abnormal shape and diameter (Fig. 4a, b). In some areas, the distorted fibril shape was apparently caused by pressure exerted from adjacent fibrils. Likewise, other fibrils with a larger diameter exhibited a lobulated shape looking like composite fibrils (Fig. 4b). Areas of loosely aggregated bundles of collagen fibrils where the banding pattern is carried across the altered collagen subunits were observed in longitudinal sections (Fig. 5). Moreover, collagen fibrils with an unraveled appearance often occurred in the areas where an altered diameter and/or a composite morphology were also found (Fig. 6).

There was a marked decrease of elastic connective tissue between the involved and the uninvolved control skin. The elastic fibers showed an altered ratio between the elastin and the microfibrilar components. The amorphous elastin component exhibited an abnormally electron-dense appearance while the microfibrils were reduced in number (Figs. 7 and 8).

A well developed fatty tissue composed of a conspicuous number of huge adipocytes of normal morphology was also seen. Embedded in this tissue, coiled secreting ends of eccrine sweat glands as well as peripheral nerve structures were observed. Although increased in number when compared with those in the same area of the uninvolved skin, the sweat glands did not show any morphological anomalies.

In the involved skin, mast cells of typical ultrastructure infiltrated the stroma.

Discussion

The Proteus syndrome is a congenital hamartomatous disorder with neurocutaneous manifestations in which epidermal, dermal and/or subcutaneous tissues are affected. Cerebriform thickening of the soles and, less often, of the palmar surface seems to be one of the most frequent pathognomonic features of this disorder.

In the affected skin of both patients, light and electron microscopy revealed a diminished number of fibroblasts with a marked reduction in cell cytoplasms and pycnotic nuclei when compared with those of the uninvolved skin. A similar hypocellularity at light microscopy level was pointed out by Pierard et al. [6] and Barkley et al. [8]. Furthermore, the involved skin showed an increased number of large adipocytes and eccrine sweat glands located between the adipose cells. Lipomatous tissue was also reported in cerebriform plantar hyperplasia by other authors [1, 2, 6]. In agreement with Pierard et al. [6] and Desai et al. [10], we also found large nerve fascicles and Schwann cells in our pathological samples.

Among the inflammatory cells infiltrate, the presence of an increased number of mast cells stood out. These cells, which are reported to produce growth factors involved in the proliferative phase of the hemangiomas, could play a role in the proliferation of the plantar hamartomatous lesions observed in our patients [11].

In the extracellular matrix of the affected skin, intermingled with normal cross-sectioned collagen fibrils, size and shape altered fibrils were seen. The concurrent distribution of fibrils with large and small diameters was also noted in the reticular dermis of individuals with Ehlers Danlos syndrome types II, III, IV, VII and VIII, cutis laxa, multicentric reticulohistiocytosis, in the early stages of dermal development in fetal skin, and in solitary collagenous connective tissue nevus [12, 13]. In longitudinal sections, two types of alterations in collagen fibrils were observed. In one type, the banding pattern is carried across the loosely integrated fibrils. This alteration has also been described as composite fibrils in the dermis of patients with Ehlers Danlos syndrome types I, II, III, VI and X [12]. In the other type, fibrils become dissociated into fine filaments that retain a banded pattern only at the point where they begin to splay out from the fibrils. This altered morphology was seen not only at the end of the fibrils but also at intervals along their length. This type of fibrils, reported by Holbrook and Byers [12] as unraveled collagen fibrils, has been recognized in the dermis of individuals with Marfan syndrome, spondyloepiphyseal dysplasia, hyalinosis cutis et mucosae, amyloidosis, shagreen patch of tuberous sclerosis and also in solar elastosis.

In our patients, on light microscopy, elastic fibril stain demonstrated elastic fibrils that were fewer than normal and fragmented. Similar observations were reported by Martínez et al. [14]. Ultrastructural examination showed alterations in the composition of the elastic fibrils, which exhibited the prevalence of an abnormally electron-dense amorphous component (elastin) with a scant amount of microfibrils. To the best of our knowledge, this finding has not been reported by other authors.

In the cerebriform plantar hyperplasia we found the three major alterations described in collagenous connective tissue at fibril level as a consequence of a gene disorder: variable diameter; unusually loose assembly in which the fibril is irregular in cross sections and varies along its length; and unraveling into filamentous subunits of varying width [12].

Taking into account that hamartoma refers to a benign, oddly arranged focal collection of histologically normal tissue indigenous to an area [15], we consider that the term composite hamartoma would be the most appropriate term to define the cerebriform plantar hyperplasia seen in the Proteus syndrome as regards the mixture of different mesodermal and neuroectodermal structures observed. Moreover, considering that the Proteus syndrome is a congenital condition characterized by multiple connective tissue hamartomas [16], it seems reasonable to consider, in view of our histopathological findings, that the CPH is distinct from a connective tissue nevus of the collagen type (collagenoma) [17] or a lipoma. Therefore, our results disagree with those reported by Martínez et al. [14], who consider this entity as a collagenoma.

The histopathological features observed in our patients, who showed a mild form of the Proteus syndrome with only a cerebriform plantar hyperplasia and macrodactyly, could provide clues for the early diagnosis of this syndrome.

Article accepted on 26/6/00

CONCLUSION

Acknowledgements

The authors thank Carolina Schlick and Santiago Dozetos for technical assistance.

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