Localized myxedema histologically mimicking spindle cell lipoma

Area of Science:

• Endocrinology
• Dermatopathology

Background:

• Graves disease is an autoimmune disorder often associated with ophthalmopathy (exophthalmos).
• Localized myxedema (pretibial myxedema) is a cutaneous manifestation of Graves disease, typically affecting the lower extremities.

Observation:

• A 55-year-old woman with Graves disease and exophthalmos presented with a recurrent foot nodule.
• Initial biopsies were interpreted as spindle cell lipoma, but recurrence prompted re-evaluation.
• Clinical presentation evolved to resemble localized myxedema, confirmed by subsequent biopsies.

Findings:

• The recurrent nodule, initially misdiagnosed as spindle cell lipoma, was ultimately diagnosed as localized myxedema.
• Clinicopathologic correlation was essential for accurate diagnosis, especially given the atypical location and initial misinterpretation.
• Standard treatment for localized myxedema resulted in significant clinical improvement.

Implications:

• Clinicians should maintain a high index of suspicion for localized myxedema in Graves disease patients with exophthalmos, even with atypical presentations.
• Localized myxedema should be considered in the differential diagnosis of spindle cell lipoma, particularly when the histology shows a myxoid stroma and the clinical course is atypical.