Integration: Unifying Concept
The gross features and changes histopathologic of sarcoidosis are distinctive in every organ in which the disease makes itself manifest. In the skin, papules consist of discrete collections of epithelioid histiocytes. Because those collections are devoid of encircling dense infiltrates of lymphocytes, they are referred to as “naked tubercles.” Plaques of subcutaneous sarcoidosis may involve the dermis in a manner just like that of papules, but, in addition, many granulomas are present within fat lobules and, to a much lesser extent, within septa.
Findings histopathologic like those of sarcoidosis in the skin are seen in lesions of sarcoidosis in organs such as lymph nodes, lung, eye, and bone. In short, sarcoidosis is a systemic granulomatous disease. Involvement of skin by sarcoidosis implies that other organs are also involved by the same pathologic process. The ichthyosiform changes of sarcoidosis usually occur on the legs in the region of the anterior tibiae and, being an expression of “acquired” ichthyosis, they exhibit histopathologic findings indistinguishable from those of ichthyosis vulgaris.
The cause of sarcoidosis is not known, but the histopathologic findings are most consonant with an infectious process.