BACKGROUND: Despite the advancements in the categorization of clinically amyopathic dermatomyositis (CADM), the classification and diagnosis of its subtypes are still challenging. The aim of our study was to describe the clinicopathological features of CADM and assess the differences between amyopathic dermatomyositis (ADM) and hypomyopathic dermatomyositis (HDM).
METHODS: This retrospective study included 43 patients with CADM diagnosed at our institution from 2016 to 2020. Patients were subclassed into ADM (n = 30) and HDM (n = 13) groups to assess their clinicopathological differences.
RESULTS: All included patients had characteristic cutaneous manifestations of dermatomyositis; 67.4% had myositis-associated auto-antibodies, including ANA (32.6%), RNP (14.0%), anti-Ro52 (9.3%), anti-p155/140 (7.0%), rheumatoid factor (7.0%), anti-NXP-2 (4.7%), anti-MDA5 (2.3%), and anti-Jo-1 (2.3%) antibodies. One patient had associated interstitial lung disease, and another patient had oral squamous cell carcinoma. The histopathological findings included mucin deposition (69.8%), telangiectasia (65.1%), lymphocytic infiltrate (48.8%), vacuolar interface dermatitis (46.5%), and epidermal atrophy (14.0%). Compared to patients with HDM, ADM patients were significantly less likely to have epidermal atrophy, 3.3% versus 38.5% (p = 0.006), and more likely to have mucin deposition, 80.0% versus 46.2% (p = 0.028).
CONCLUSIONS: We described the clinicopathological features of CADM and highlighted the distinctions between ADM and HDM dermatopathologic findings. This information may prove helpful in diagnosing ambiguous lesions.

Dermatomyositis is associated with malignancies and is known to have systemic involvement. However, associations with bone diseases have not been well described in the current literature. This article describes the second reported case of the co-existence of dermatomyositis and Paget\'s Disease of Bone (PDB), but is the first report to describe such co-existence in a specific subtype of dermatomyositis - hypomyopathic dermatomyositis. Our patient was a 51-year-old woman who presented with prolonged fever, myalgia, morning stiffness, and rashes pathognomonic of dermatomyositis. There was no muscle weakness clinically, although muscle enzymes were raised and electromyogram revealed myopathic changes. Further imaging showed the incidental finding of a T11 vertebral bone lesion, of which biopsy confirmed the diagnosis of PDB. Our report illustrates the diagnostic approach to bone lesions in patients with dermatomyositis, and takes a closer look at the pathophysiology and management implications of the co-occurrence of these two rare diseases.

Hypomyopathic dermatomyositis (DM) presents with cutaneous lesions consistent with dermatomyositis but in the absence of clinically appreciable muscle weakness. The cutaneous manifestations are often refractory and more resistant to conventional therapy than concomitant muscle involvement. We present a 61-year-old hypomyopathic patient with DM who failed to respond to standard therapy but was successfully treated by low-dose interleukin-2 (IL-2) with no significant side effects. We conclude that low-dose IL-2 is a safe and effective treatment for hypomyopathic DM.