Invisible dermatoses from the perspective of the dermatopathologist: new observations

The term "invisible dermatoses" is often used in two different contexts: 1) dermatoses which are invisible to the clinician, i.e., diseases with no significant clinical features; 2) dermatoses which are invisible to the pathologist. These latter comprise a wide spectrum of entities which present with definite and obvious clinical features, but subtle or hidden histological features and are therefore "invisible" histologically. Diagnosis of such diseases represents a great challenge to both the dermatologist and dermatopathologist. The list of such diseases, originally comprising only few entities, has been gradually expanded over decades and now is a large one. This review focuses on the recently expanded spectrum of such diseases, and offers to the dermatopathologist a strategy for their diagnosis, based mainly on proper awareness, recognition of subtle features, special stains, special investigations such as immunofluorescence and histochemistry and proper clinicopathological correlation.