Invisible Dermatoses from the perspective of the dermatopathologist. Original observations and novel concepts.

The phrase 'invisible dermatoses' has been used in two different contexts: 1) Invisible dermatoses to the clinician, i.e., diseases with no significant clinical features, 2) invisible dermatoses 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

Septic vasculitis and vasculopathy in some infectious emergencies: the perspective of the histopathologist

Sepsis is a potentially life-threatening complication of an infection where cutaneous lesions often represent one of the early signs. A myriad of microorganisms including bacteria, fungi, yeasts, viruses, protozoas, helminths and algae can be implicated. A broad spectrum of clinical and histopathologic findings can be observed in the skin and the common denominator is a thrombotic vasculopathy. The pathogenesis of cutaneous septic vasculitis (SV)/vasculopathy is complex and includes five main mechanisms: disseminated intravascular coagulation, direct invasion and occlusion of blood vessel walls by microorganisms, hypersensitivity reaction with immune complex deposition into blood vessel walls, embolism from a distant infectious site and vascular effects of toxins. Herein we describe the clinicopathologic findings of some selected cases of SV recently observed in our hospital, including purpura fulminans, necrotizing fasciitis, cutaneous meningococcemia, malignant syphilis and disseminated alternaria infection. Histopathologically, a wide spectrum of histopathologic changes was observed in skin specimens from the various entities, involving the intensity and composition of the inflammatory infiltrate, the degree of vascular changes and the presence of microorganisms, that ranged from a predominant not inflammatory, thrombotic-occlusive vasculopathy in purpura fulminans to leukocytoclastic vasculitis like changes in cutaneous meningococcemia to a dermal angiomatosis-like pattern in disseminated Alternaria infection. The different pathologic presentations may be related to the microorganism involved, the main pathogenetic mechanism that induced the vascular injury and the individual immunologic burden. Early skin biopsy for histopathologic examination and microbiologic culture is a cornerstone in the diagnosis of life-threatening diseases that present with cutaneous septic vasculitis. Ancillary techniques, such as immunohistochemistry and polymerase chain reaction are additional novel and helpful tools to identify pathogens, leading to definite diagnosis in cases with challenging or ambiguous clinical and/or pathologic findings