During the early stage of generalized morphea there is an inflammatory reaction involving primarily the fat around the eccrine sweat glands and the subcutaneous tissue. The cellular infiltrate consist of lymphocytes, plasma cells, and histocytic type cells. Lymphoid follicles with germinal centers were also noted. The inflammatory stage is followed by the replacement of the subcutaneous tissue by hyalinized connective tissue. This process is probably responsible for the skin induration in this disease.
Fleischmajer R, Nedwich A. Generalized MorpheaI. Histology of the Dermis and Subcutaneous Tissue. Arch Dermatol. 1972;106(4):509-514. doi:10.1001/archderm.1972.01620130041010