[Endogenous skin overloads]

As in other organs, the diagnosis of endogenous cutaneous overload diseases is based on histopathological analysis of the lesions using special stainings, even if the clinical appearance is sometimes very suggestive. The lesions are sometimes very subtle and can be included in the group of "invisible" dermatoses, such as primary macular cutaneous amyloidosis or calciphylaxis. Superficial dermal melanosis or pigmentary incontinence generally reflects the post-inflammatory stage of a chronic or recurrent interface dermatitis. Section levels should be systematically performed to look for active lesions of diagnostic interest: Alcian blue staining to identify dermal mucinosis (connectivitis) and pan-T markers (fixed pigmented erythema, lichenoid mycosis fungoides, and vitiligo). Some pathologies have a prognostic impact, either because they reflect an underlying disease, monoclonal gammopathies, in particular myeloma, being one of the most common conditions in this context (AL amyloidosis, xanthoma and xanthogranuloma, scleromyxedema), or because they can be associated with visceral damage (AL amyloidosis, scleromyxedema). The clinical-pathological comparison is mandatory to rule out differential diagnoses, especially for life-threatening diseases: nodular amyloidosis and primary cutaneous amyloidosis versus systemic AL amyloidosis, papular mucinosis versus scleromyxedema and calcific panniculitis versus calciphylaxis.