The study presents observations of biopsies from 47 patients with cutaneous sarcoidosis and 45 patients with tuberculoid leprosy. Epidermal changes showing parakeratosis, liquefaction degeneration, and glycogen occur more frequently in sarcoidosis. Nerve invasion is seen only in tuberculoid leprosy. Infiltration of arrectores pilorum muscles frequently occurs in tuberculoid leprosy and is rare in sarcoidosis. Fibrinoid degeneration within tubercles is common in sarcoidosis and absent in tuberculoid leprosy. Attachment of tubercles to the epidermis, sharp margination of the tubercles, and naked-appearing tubercles are seen more frequently in sarcoidosis than in tuberculoid leprosy. Elongateshaped tubercles and lymphocytes within, and forming a mantle about, tubercles are prominent and seen more frequently in tuberculoid leprosy. Cutaneous sarcoidosis and tuberculoid leprosy show similar microscopic features, but distinction can be made on the basis of critical histopathologic and histochemical evaluation.
Ramasoota T, Johnson WC, Graham JH. Cutaneous Sarcoidosis and Tuberculoid LeprosyA Comparative Histopathologic and Histochemical Study. Arch Dermatol. 1967;96(3):259-268. doi:10.1001/archderm.1967.01610030037006