Middle-aged Woman With a Soft Lesion on the Leg
What's Your Diagnosis
HISTORY
A healthy 50-year-old woman presents for a routine skin cancer screening. During the physical examination, she mentions that she has had a lesion on her left leg for at least 30 years (A). It has never been biopsied or treated in the past. Occasionally, the lesion will “fill with blood” if traumatized, but it is otherwise asymptomatic. Transillumination reveals transmission of light through the papule (B). Her past medical history is significant for treated hypothyroidism and vitamin D deficiency.
WHAT’S YOUR DIAGNOSIS?
(Answer and discussion on next page)
ANSWER: Cutaneous focal mucinosis in the setting of hypothyroidism
BACKGROUND
Dermal mucin is an amorphous gelatinous substance normally produced by cutaneous fibroblasts. Chemically it consists of acid glycosaminoglycans. These complex carbohydrates are free-floating or may be fixed on both sides of a protein core (proteoglycan monomer). In the dermal mucinoses, the fibroblasts are stimulated to produce greater quantities of acid glycosaminoglycans.
Figure – This skin-colored papule had been present for at least 30 years on the leg of a woman with treated hypothyroidism. Cutaneous focal mucinosis was diagnosed on the basis of histologic examination.
The cutaneous or dermal mucinoses are a heterogeneous group of connective tissue disorders in which an abnormal amount of mucin accumulates in the skin, either diffusely or focally. They have a number of different morphologic presentations and can often be confused with other diseases. The mucinosis may be a primary process, in which mucin deposition is the major histologic finding, or a secondary process, in which mucin represents an associated histologic finding. The primary mucinoses are further divided into degenerative inflammatory and neoplastic-hamartomatous forms.
Cutaneous focal mucinosis (CFM) is a benign form of primary cutaneous mucinosis that is specifically described as a de-generative inflammatory mucinosis. It is a rare condition characterized by asymptomatic singular dermal mucin deposition and histopathologic homogenous mucin deposition in the dermis.1
CLINICAL FEATURES
Clinically, CFM presents as a skin-colored to white papule or nodule, generally less than 1 cm in diameter (Figure). The lesions are usually asymptomatic and have a smooth surface. They most commonly occur on the trunk or extremities but may present anywhere on the body, including the oral cavity. CFM generally affects adults, with an average age of 38 years in either sex.
PATHOGENESIS
The pathogenesis of cutaneous mucinosis is not well understood. Studies have suggested that an unknown circulating factor may stimulate fibroblasts. This has been described as a “muciparous” reaction of the connective tissue to external non-specific stimuli. Chronic antigenic stimulation, inflammation, viral infections, or inherited abnormalities could account for the changes.2
In contrast to other cutaneous mucinoses, CFM is not usually associated with systemic abnormalities. To our knowledge, only two documented cases link CFM to hypothyroidism, as in this patient.3
DIAGNOSIS
Because of the rarity of CFM and the non-specific clinical findings, this lesion is often mistaken for other disorders such as dermal cysts, nevi, myxomas, and xanthomas. The diagnosis is a histologic one. Tissue examination reveals a slightly elevated, dome-shaped dermal nodule characterized by an abundant, focal, but not sharply demarcated “pool” of mucin filling the whole dermis.4
TREATMENT
The treatment of choice for CFM is simple surgical excision. Relapses are generally uncommon. In this patient, a shave biopsy was performed with no complications. She was subsequently lost to follow-up.
REFERENCES:
1.Rongioletti F, Rebora A. Cutaneous mucinoses: microscopic criteria for diagnosis. Am J Dermatopathol. 2001;23(3):257-267.
2.Wilk M, Schmoeckel C. Cutaneous focal mucinosis: a histopathological and immunohistochemical analysis of 11 cases. J Cutan Pathol. 1994;21(5):446-452.
3.Jakubovic HR, Salama SSS, Rosenthal D. Multiple cutaneous focal mucinosis with hypothyroidism. Ann Intern Med. 1982;96(1):56-58.
4.Johnson WC, Helwig EB. Cutaneous focal mucinosis: a clinicopathological and histochemical study. Arch Dermatol. 1966;93(1):13-20.