Amyopathic Dermatomyositis Presenting With Oral Mucocutaneous Lesion and No Muscle Involvement in an Elderly Woman: A Mimicry of Fungal Infection and Eczema

Amyopathic dermatomyositis (ADM) is a rare subtype of dermatomyositis defined by characteristic cutaneous findings without clinical or laboratory evidence of muscle involvement for at least six months. Although lacking myopathy, patients remain at risk for systemic complications, particularly rapidly progressive interstitial lung disease (RP-ILD) in the presence of anti-melanoma differentiation-associated gene 5 (MDA5) antibodies, as well as autoimmune overlap and malignancy. Diagnostic recognition may be delayed due to subtle clinical features and non-specific biopsy results. We report a 76-year-old woman who presented with violaceous papules on the upper and lower extremities, a painless blister on the lateral tongue, and purplish discoloration of the right great toe. Initial biopsy of the oral lesion was non-specific, and differential diagnoses included eczema and fungal infection. Her symptoms persisted despite empiric topical steroids and antifungal therapy. Repeat biopsies and exclusion of muscle disease confirmed ADM. Systemic corticosteroids and hydroxychloroquine were initiated, followed by mycophenolate mofetil, with limited response. The addition of intravenous immunoglobulin (IVIG) resulted in gradual improvement, leading to complete resolution of cutaneous lesions after 18 months, without systemic complications. This case illustrates the atypical presentation of ADM and the challenges in establishing an early diagnosis when muscle involvement is absent. It highlights IVIG as an effective option for treatment-resistant disease and underscores the importance of maintaining a high index of suspicion, pursuing thorough diagnostic evaluation, and ensuring long-term monitoring for interstitial lung disease and malignancy, even in patients who present with isolated cutaneous findings.