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localized scleroderma

Friday 16 November 2012

Localized scleroderma is the most common form of scleroderma.

It generally occurs in children and young adults and there is a female preponderance.

Neonatal onset has been recorded.

There is no visceral involvement or Raynaud’s phenomenon and it usually has a self-limiting course. Progression to or coexistence of the systemic form is rare.

Antinuclear antibodies are uncommon except in the linear form.

Microscopy

Localized scleroderma is characterized by three outstanding features:
- the deposition of collagen in the dermis and subcutis,
- vascular changes,
- an inflammatory cell infiltrate, particularly in early lesions.

The epidermis may be normal, somewhat atrophic, or even slightly thicker than usual.

The dermis is increased in thickness and composed of broad sclerotic collagen bundles which stain strongly with the trichrome stain.

Collagen also replaces the fat around the sweat glands and extends into the subcutis.

In the latter site, the collagen is homogenized and less compact than in the dermis and it shows only weak birefringence and trichrome staining; there is an increased number of fibroblasts.

However, the collagen in the subcutis stains strongly with the PAS stain in contrast to the very weak staining of that in the dermis. Mucopolysaccharides are present in the early lesions, particularly in the subcutis. Rarely, a secondary cutaneous mucinosis, with significant interstitial mucin, is present.

In most cases of morphea, the thickened collagen bundles are in the mid and deep reticular dermis.

There is atrophy of adnexal structures, particularly the pilosebaceous units. Eccrine glands are situated at a relatively high level in the dermis as a result of the collagen deposited below them. The arrectores pilorum are often hypertrophied. The mesenchymal elements of peripheral nerves are involved in the sclerotic process.

The vascular changes are thickening of the walls of small blood vessels and narrowing of their lumen. In small arteries there is fibromucinous thickening of the intima.

The inflammatory cell infiltrate is composed of lymphocytes with some macrophages and plasma cells. It is distributed around blood vessels or more diffusely through the lower dermis and subcutis, particularly at the border of early lesions.

The infiltrate is more marked in localized scleroderma than systemic scleroderma and in early rather than late lesions. The infiltrate is rarely heavy.

Immunohistochemical characterization of the infiltrate has shown the presence of T lymphocytes of both CD4 and CD8 subtype, as well as Langerhans cells and natural killer cells.