Case Presentation: A 36-year-old Laotian female with a history of hypothyroidism presented with 3 days of worsening symmetrical proximal muscle weakness and anasarca. She was recently seen at another hospital and presented with one day of worsening throat swelling and diffuse anasarca. Over the next 2 months, she developed dysphagia requiring gastrostomy tube and was discharged with an unclear diagnosis. She then presented with disabling weakness in her arms and legs. Physical exam revealed significantly weak muscle strength accompanied with erythema of the lower back. Laboratory studies were significant for creatinine kinase of 925 U/L, aldolase of 15.6 U/L,and positive anti-NXP-2 antibody (Ab). ANA, Anti-Smith/Anti-DNA, Anti-Jo, AChR antibodies were negative. A muscle biopsy demonstrated non-specific inflammatory changes with lymphocytic infiltrates. MRI findings were consistent with myositis. Pt was then diagnosed with Anti-NXP2 Ab Dermatomyositis (DM). Malignancy screening was negative except for abdominal CT that revealed swelling of bowel wall and a dermoid cyst.She was started on high-dose corticosteroids followed by pulse-dose steroids, IV immunoglobulin, and plasma exchange. Patient also underwent dermoid cyst removal surgery. However, her symptoms continued to persist with worsening soft tissue swelling, myalgia, and weakness with development of heliotrope rash and shawl’s sign. She was given rituximab with no response and started on Tolfacitinib.
Discussion: DM has a prevalence ranging from 0.005 to 0.02% with a 2 to 1 female predominance [1]. The prevalence of anti-NXP-2 Ab among patients with DM varies from 11% to 30%. Dysphagia, calcinosis, diffuse soft tissue swelling, myalgia, and mild skin involvement are common presenting symptoms, which are consistent with our case aside from the calcinosis [2-4]. Cancer prevalence in DM varies and many patients develop cancer within 3 years following diagnosis [5]. In a study of colorectal cancer and DM, removal of the tumor lead to complete resolution of DM in about 54% (14/26) [6]. An extensive workup, including a whole-body PET/CT scan, was negative for cancer in our patient and she failed to improve after removal of the dermoid cyst, which was thought to be causing a paraneoplastic syndrome. Although DM has been historically associated with cancer, this association was no proven in a recent meta-analysis[7]. Corticosteroids are the cornerstone of myositis treatment, with up to 60% of patients showing some response, though there is no evidence to support the choice of corticosteroid sparing agents in the treatment of steroid-resistant DM [8]. In our patient, there was no response despite several modalities of immunosuppresants. More studies are needed to further characterize this subset of DM.
Conclusions: Proximal muscle weakness is a very common chief complaint with multiple differentials. Anti-NXP2- Ab DM remains a very rare condition and recognition is important for appropriate workup, diagnosis, and management. Appropriate cancer screening up to 3 years following diagnosis of DM is paramount.