P11-Dermatomyositis

S5C20aP13a-2: The mucinosis of collagen-vascular disease (dermatomyositis) is represented. Green arrows point to preserved elastic fibers. Red arrows identify collagen bundles in the process of unbundling to become individual (unit) fibrils.

S5C20aP13a-3: A cell-poor lichenoid reaction is represented; features include mild hyperkeratosis, a straight dermal-epidermal interface, and vacuolar changes, mainly on the epidermal side of the basement membrane. The basement membrane is only slightly broadened. There are cytopathic changes in the basal layer of the epidermis; a cluster of necrotic keratinocytes is present in the epidermis above the basal layer in the center of the field. The cells of the superficial unit are hypertrophied. There is no component, other than a basal layer of cells, that might be characterized as a basal unit (the basic patterns is that of a cell-poor reaction with atrophy of the basal unit [no rete ridges] and cytopathic changes. There are occasional patterns of “satellite cell necrosis.” The patterns are LE-like, but differ somewhat from classic examples of LE. In addition to the above features, the papillary dermis is widened and hyalinized. The reticular dermis shows atrophy of collagen bundles and widening of spaces among the bundles (mucinosis). Fibrinoid necrosis of small vessels (an uncommon feature) (red arrows) and fibrin deposits among collagen bundles (fibrinoid degeneration of collagen-vascular diseases) (green arrows) are additional features. The patterns are compatible with dermatomyositis.


S5C20aP13a-1: In this lesion of dermatomyositis, the patterns in the epidermis and at the dermal-epidermal interface are those of a cell-poor lichenoid process. The epidermis is atrophic (as is the basal unit of the epidermis); it is thin and appears to be compressed (keratinocytes of superficial unit are thin). The basal layer is poorly defined; it shows cytopathic changes with lysis of cells and scattered, necrotic keratinocytes (apoptosis). Scattered, necrotic keratinocytes (colloid bodies) are present in the upper portion of the dermis. Collagen bundles are fibrillated and the interstitial matrix is mucinous (mucinosis) .

S5C20aP13a-4: In this field, fibrinoid “degeneration” is a prominent feature of the mucinous collagenosis (mucinosis, normal collagen patterns, and sclerosis are but variations along a spectrum).

S5C20aP13a-5: The interface between the dermis and subcutaneous fat is represented. The subcutaneous tissue at the bottom of the field shows some degree of lipoatrophy with a reduction in the size of lipocytes and an increased prominence of small vessels. The dermis shows atrophy of collagen bundles and a mucinous interstitium (mucinosis). There are minimal perivascular infiltrates of lymphocytes (dermatomyositis).

S5C20aP13a-6: In this area of the myositis of dermatomyositis, there are interstitial infiltrates of lymphocytes and histiocytes.

S5C20aP13a-7 (dermatomyositis): In another field, some of the skeletal muscle fibers are swollen and pale. Lymphocytes and histiocytes have migrated into the sarcoplasm; they appear to be naked nuclei surrounded by vacuoles (green arrows). Some of the fibers are more brightly acidophilic; they show disruption of the sarcoplasm (floccular degeneration) (red arrows).

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