The dermal reaction pattern refers to those papules, plaques, and nodules that do not have epidermal changes, such as scales.
Smooth primary lesions (papules, nodules, plaques) = dermal reaction pattern.
The substance of dermal reaction pattern primary lesions may be made up of cells in the dermis or a dermal deposit. These cells may be inflammatory in nature (such as lymphocytes in lymphocytoma cutis or granulomas in sarcoidosis) or neoplastic, in which case they may be either benign (such as nevi or benign tumors arising from appendageal structures) or malignant (such as basal cell cancers, squamous cell cancers, melanomas, or cutaneous metastases). Dermal deposits, including urate, calcium, or mucin, may also give rise to these smooth primary lesions. Alterations in dermal collagen or elastic fibers, such as scleroderma or morphea, constitute a third category in this reaction pattern.
Papules, Nodules, and Plaques in the Dermal Reaction Pattern may be Composed of any or all of the Following Dermal Components:
The sclerotic plaques of scleroderma or morphea are firm to palpation and may be either slightly elevated or depressed.
Dermal plaques may be raised or depressed, as is seen in sclerotic conditions such as scleroderma and morphea.
A final group in this reaction pattern is diseases that are deep to the dermis. Subcutaneous disease, such as panniculitides and subcutaneous granulomatous disease or neoplasms, also gives rise to smooth nodules. Therefore, subcutaneous dermatoses can be categorized in the dermal reaction pattern. Conditions arising from other soft tissue structures may also present as smooth nodules without surface change. Examples include nodular fasciitis that arises from the fascial plane, bursae, and giant cell tumor of the tendon sheath.
Subcutaneous diseases and conditions arising from other soft tissue structures are also classified as dermal reaction pattern as they manifest as smooth nodules.
Some dermal infiltrates are not classified in the dermal reaction pattern. Deep fungal infections, such as chromomycosis, may often have overlying epidermal changes, such as a hyperplastic epidermis and scale and, if so, present clinically as the papulosquamous reaction pattern. Some dermal infiltrates are so minimal as to create macules rather than papules, nodules, or plaques. An example here is telangiectasia macularis eruptiva perstans (TMEP), a form of cutaneous mastocytosis with minimal infiltration of the dermis by mast cells and lesions that appear as red macules. The macules of TMEP therefore may fall preferentially into the vascular (red) reaction pattern (see Chapter 10). Urticaria pigmentosa, another variant of cutaneous mastocytosis, may present as brownish smooth papules that allow it to be classified as dermal; however, sometimes the papular component is absent and the primary lesion therefore manifests as a macule. In this case, invoking the brown differential diagnosis will allow for ...