Pretibial Mucin: Histologic Patterns and Clinical Correlation

Background and Objective: We identified several patients with a histologic diagnosis of pretibial myxedema in whom thyroid disease was not found. The purpose of this study was to investigate if histologic characteristics can distinguish between pretibial mucinosis secondary to Graves’ disease and that unassociated with thyroid disease. Methods: Biopsy specimens interpreted as compatible with pretibial myxedema were reviewed; these included 12 cases of pretibial mucinosis with documented Graves’ disease, and six cases of pretibial mucinosis without evidence of Graves’ disease. Ten specimens interpreted as compatible with stasis dermatitis were also evaluated for histologic characteristics, including the possible presence of mucin. Results: Features that distinguish between pretibial mucinosis associated with Graves’ disease and pretibial mucinosis without Graves’ disease included preservation of a zone of normal-appearing collagen in the superficial papillary dermis (12/12 with Graves’ disease, 0/6 without), mucin deposition in the reticular dermis (12/12 with Graves’ disease, 0/6 without), lack of mucin deposition in the superficial papillary dermis (11/12 with Graves’ disease, 1/6 without), angioplasia (2/12 with Graves’ disease, 6/6 without), and the presence of hemosiderin (2/12 with Graves’ disease, 6/6 without). Mucin deposition in the papillary dermis was found in six of 10 specimens interpreted as stasis dermatitis. Conclusions: There are patients with pretibial mucinosis in whom there is no thyroid disease. Specimens from patients without Graves’ disease have features of stasis dermatitis in addition to mucinosis. We conclude that pretibial mucinosis may result from stasis or Graves’ disease and that histologic differences allow for accurate differentiation.