[Atypical papular mucinosis with initial histological findings evocative of granuloma annulare]

Papular mucinosis is characterized by primary reticular dermal mucin deposition in the absence of any thyroid abnormalities. There is extensive clinical variety in this disease, from benign localized forms to generalized forms, on occasion lethal. The current classification was established in 1991 in order to allow identification of these generalized forms of the disease and help ensure a better therapeutic approach. We report the case of a patient with atypical papular mucinosis having initial histological features consistent with granuloma annulare.

A 55-year-old man consulted for a papular eruption of the hands. A diagnosis of granuloma annulare was initially made because of misleading histological findings. However, the eruption spread to the inner thighs and the hypogastric area despite dermocorticoid therapy. Laboratory evaluation showed a monoclonal gammopathy. Further biopsies revealed diffuse dermal mucin deposits. We finally concluded on atypical localized papular mucinosis.

Papular mucinosis is a rare disease and its physiopathology remains to be elucidated. The diagnostic criteria are sometimes inadequate, and its classification includes both atypical and intermediate forms. Our case belongs to the latter class because of its extensive and unusual topography, and its association with a monoclonal gammopathy. Although granuloma annulare is not a classical differential diagnosis, two other cases with similar histological findings have already been published.