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NXP-2 Positive Dermatomyositis: A Unique Clinical Presentation

Dermatomyositis (DM), a myopathy associated with inflammation and muscle weakness, has historically been difficult to diagnose. Recently, nuclear matrix protein (NXP-2) antibodies have been described as a myositis-specific antibody that may aid in the diagnostic evaluation. We present the case of a 21-year-old, previously healthy, African American male with DM. He presented to our outpatient clinic with periorbital swelling and a rash, for which he was started on prednisone by an ophthalmologist. Towards the end of the prednisone taper, he began to experience muscle weakness, a worsening rash, and dysphagia to solids with a resultant loss of 60 pounds within a month. He was transferred to a tertiary care hospital where he was further evaluated and ultimately diagnosed with dermatomyositis, supported by skin and muscle biopsies, and was found to be positive for NXP-2. He was given intravenous immunoglobulin (IVIG) and high-dose steroids with improvement.


Introduction
Dermatomyositis (DM) is a systemic disease characterized by chronic inflammation of the skin and muscle [1,2]. There is significant clinical heterogeneity with respect to lung, muscle, joint, and cutaneous involvement, as well as variability in its association with malignancy and response to therapy [2][3][4][5]. Many patients with DM have circulating antibodies which are often associated with distinct clinical phenotypes [6,7].
Here we present a case of adult NXP-2 positive DM.

Case Presentation
A 21-year-old African American male with no past medical history was in his usual state of health until January 2014, when he developed unusual periorbital swelling and a rash. He was evaluated at an outpatient ophthalmology clinic and was started on 60 mg prednisone daily. His periorbital swelling improved with this therapy, but as the prednisone was tapered he began experiencing symmetric bilateral proximal muscle weakness and soreness of the upper and lower extremities. This was accompanied by a hyperpigmented rash on the trunk, extensor surface of the arms, and upper thighs with associated soft tissue swelling. Two weeks after the completion of the prednisone taper, he began experiencing dysphagia to solids more than to liquids and suffered several choking episodes. This forced a change in his diet to thick liquids; as a result, by the end of the month he had lost 60 pounds. Given his worsening symptoms, he presented to our outpatient clinic in July 2014. Blood work for autoantibodies  Figure 1: On physical exam, the patient was found to have a patchy, raised, nonulcerative healing rash with hypopigmentation on bilateral arms and forearms and anterior and lateral thighs, a patch of hyperpigmented rash on chest, and a diffuse rash over abdomen.
including ANA and dsDNA was negative. He was found to have an elevated total CK (1274 IU/L). ESR and CRP were normal. An upper endoscopy did not reveal any structural abnormalities.
In August 2014 during a follow-up visit at our clinic he was found to be very weak, barely able to climb stairs or stand up from a seated position. On examination, hyperpigmented pruritic frank macules were noted on the extensor surface of his arms, trunk, and upper thighs in multiple phases of healing ( Figure 1). His hands and lips were swollen. Hand grip strength was reduced bilaterally. He had 3/5 strength in the left upper extremity and 4/5 on the right upper extremity. He was not able to raise his arm above his head; muscle bulk was decreased in the upper arm compared to the lower extremity. Hip flexors were 3/5 bilaterally, but quadriceps and hamstrings were 4/5 (Table 1). In this setting he was immediately transferred to a tertiary care facility.
Initial lab work there revealed elevated enzymes with AST of 75 U/L, creatinine kinase level of 1017 IU/L, myoglobin level of 233 ng/mL, LDH level of 386 U/L, ferritin 3151 ng/mL and ESR 33 mm/hr, uric acid 6.8 mg/dL, and being HIV negative (Table 1). Based on the clinical presentation and history, inflammatory myositis was suspected and rheumatology and dermatology were consulted. Blood works including an ANA, anti-Jo-1, anti-Ro, anti-La, anti-RNP/Smith, serum myoglobin, aldolase, CMV/EBV titers, and anti-histone antibodies were all negative.
He underwent CT scan and MRI of his chest, abdomen, and pelvis. Edema found in the bowel wall on CT (Figure 2(a)) prompted a colonoscopy with biopsy but results were nonspecific. MRI revealed intramuscular and subcutaneous edema (Figure 2(b)), but no occult malignancy. Skin biopsies were obtained from his right extensor arm and anterior chest which revealed a vacuolar interface dermatitis with dermal mucin deposition. A muscle biopsy of his left biceps demonstrated perifascicular atrophy and inflammation consistent with dermatomyositis. For his dysphagia, he was evaluated by a speech-language pathologist and underwent a cine esophagram which showed severe swallowing weakness with aspiration; a PEG tube was subsequently placed. He then began therapy with IVIG and pulse-dose pulse steroids with an eventual taper to 60 mg prednisone. Following IVIG treatment his hemoglobin dropped to 6.9 mg/dL with an

Discussion
Dermatomyositis is a systemic disease that can be difficult to diagnose in its early stages [5]. The presence of myositisspecific autoantibodies allows for a more confident diagnosis, Case Reports in Rheumatology better phenotype classification, and potentially more targeted treatments. Herein we present a patient with NXP-2 positive DM with dysphagia, unusual bowel wall edema, and diffuse soft tissue and muscle inflammation responsive to IVIG and corticosteroids. Anti-NXP-2 antibodies were originally described in a subset of patients with juvenile DM and were associated with severe muscle weakness, polyarthritis, joint contractures, and intestinal vasculitis [7]. Anti-NXP-2 is also strongly associated with malignancy [8]. Until recently, there has been limited literature regarding its association in adult DM.
A recent study showed 1.6% of adult Japanese patients with inflammatory myopathy had anti-NXP-2 antibodies [9]. Anti-NXP-2 antibodies were found to be the most prevalent specificity in an Italian cohort followed by other known MSAs, such as anti-Jo-1 and Mi-2, and it was found to be similar to two juvenile DM studies performed in Argentina, the United Kingdom, and Ireland [7].
Two recently published studies have demonstrated that NXP-2 autoantibodies are associated with dysphagia and soft tissue/peripheral edema. Rogers et al. observed that in 20 patients with antibodies to NXP-2 dysphagia and peripheral edema were present in 74% and 35%, respectively [10]. In another study by Albayda et al., dysphagia and subcutaneous edema were present in 62% and 36% of anti-NXP-2 positive adult dermatomyositis patients [11]. In both studies, patients negative for NXP-2 autoantibodies had significantly less dysphagia and peripheral edema.
We describe a case of NXP-2 positive DM in a 21-year-old African American man with gastrointestinal involvement and soft tissue edema. This adds to the growing body of evidence that NXP-2 antibodies may reflect a unique phenotype of DM.

Conflicts of Interest
The authors declare no conflicts of interest.