Induration

Definition
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Circumscribed, 0.2-10.0 cm large (or larger), solitary or multiple, localized, disseminated, rarely generalized increases in skin consistency. Indurations of the skin are not actual efflorescences according to the nomenclatures valid up to now. However, indurations are symptoms which have great diagnostic significance and must be recorded as such. The term induration describes a tactile finding which is clearly distinguished from the healthy environment by an increase in consistency.

General information
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Indurations can be of different colours and are distinguished from plaque by their remaining in the skin level. The induration can be distinguished from a plaque by the palpatory findings. A spot is characterized by the fact that "nothing" is felt, neither a skin rupture (= plaque) nor an increase in consistency (= induration).

Pathogenetically, an induration of the skin may be based on different processes. Indurations of the skin and also of the subcutis are observed in circumscribed scleroderma (morphea) and progressive systemic scleroderma. Morphea is based on skin sclerosis. This is the accumulation of increased collagen in an altered arrangement and fibrous structure with homogenized eosinophilic aspect and reduced number of fibroblasts. This results in characteristic structural changes of the collagen fibres (increase and thickening of the collagen fibre bundles) and a shrinking of the tissue. In sclerosis, the skin is circumscribed or diffusely hardened, compact, with simultaneous loss of elasticity. In sclerödema adultorum Buschke there is massive accumulation of proteoglycans and thus an extensive, solid increase in the consistency of the skin.

The diffuse, fibrosing nephrogenic dermatopathy, which is a consequence of chronic terminal renal insufficiency, leads to an extensive, almost wood-like solid induration of skin and subcutis due to increased collagen production. The chewing of betel nuts, which is frequently practiced in India, can lead to an extensive induration of the oral mucosa which is still etiopathogenetically unclear.

A deep induration affects the subcutis and/or the underlying structures such as fascia and muscles. The term induration describes a palpation finding that is clearly differentiated from the healthy environment by increasing its consistency. A deep induration can be plate-like or spherical (see nodes below), dolent or indolent. The overlying skin may present itself as completely normal or also changed (e.g. reddened). A typical example of a plate-like deep induration is Shulman's syndrome, a fascitis associated with eosinophilia. In deep circumscript scleroderma, plate-like, sometimes nodular, deep indurations can also be detected.