Histologic clues that facilitate rapid diagnosis of morphea at scanning magnification have been described but not well studied. We examined 73 cases of morphea and 42 control cases to determine the sensitivity and specificity of a novel histopathological feature—“the line sign (LS)”—a prominent, straight interface between subcutis and adjacent collagen. The sensitivity of LS was shown to be the most sensitive feature among 4 other existing histopathological features. Its specificity, however, was not the highest among the other features and needs to be evaluated further in future studies to confirm the usefulness of LS as a diagnostic tool for morphea.

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BackgroundThe Floating Sign is a histopathologic clue to the diagnosis of autoimmune sclerosing skin disorders such as morphea and interstitial granulomatous dermatitis (IGD). On the other hand, the “free‐floating” sign has been associated with neoplasms, for example, dermatofibroma and interstitial mycosis fungoides. Herein, we report the Free Sign in sclerosing skin disorders.MethodsIn a case‐control study, we applied detailed histopathologic definitions of Floating Sign and Free Sign to assess their presence in morphea, IGD, and other sclerosing disorders.ResultsFree Sign was present in most cases of morphea (46/55, 84%) and IGD (7/13, 54%) but not necrobiosis lipoidica (NL) (6/14, 42.8%) or sclerodermoid graft versus host disease (SGVHD) (2/7, 28.5%). The sensitivity and specificity of Free Sign for morphea versus other disorders was 84% and 56%, respectively. Floating Sign was not identified in most cases: NL (3/14, 21.4%), SGVHD (1/7, 14.2%), morphea (5/55, 9%), IGD (1/13, 7.7%). The diagnostic sensitivity of Floating Sign in morphea was 9%.ConclusionsThe Free Sign was present in most cases of morphea in our series and may represent a clue to the presence of evolving sclerosis. Free Sign may be seen in other sclerosing disorders. Technical artifact is a potential cause of a false‐positive Free Sign.

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