Nuclear matrix protein 2 antibody-positive dermatomyositis associated with hepatocellular carcinoma

myopathy

Gastroenterology Department for treatment. On admission day, a significant decrease in muscle strength in the extremities was observed, and the patient was referred to the Department of Rheumatic Diseases for further testing. Two weeks before hospitalization, he had difficulty lifting objects. His muscle weakness progressed, and difficulty in swallowing occurred several days before hospitalization. He had no history of fever, dyspnoea, cough or myalgia. His medical history included diabetes mellitus and hypercholesterolaemia. His current medical prescriptions included metformin, dapagliflozin, linagliptin and pravastatin. He had a 10-year history of smoking and drank socially. He had no known family history of rheumatic diseases. A physical examination revealed multifocal pruritic, erythematous plaques on the extremities and trunk (Fig. 1B), and no skin lesions typically associated with DM, such as heliotrope rash or Gottron's sign, were observed. A musculoskeletal examination found grade 3-4/5 muscle strength in the symmetrically proximal and distal muscles of the bilateral upper extremities. Autoantibodies, including anti-SSA, anti-SSB, anti-RNP, anti-Sm, anti-dsDNA, anti-Jo-1, anti-PL-7, anti-PL-12, anti-EJ, anti-OJ, anti-KS, anti-Mi2, anti-SAE and anti-TIF1-gamma were negative, but anti-NXP-2 antibody was positive. MRI of both lower extremities revealed areas of high signal intensity in the bilateral thigh muscles. No skin or muscle biopsy was performed. HCC-associated DM was diagnosed on the basis of these findings. Pravastatin was discontinued, and treatment with prednisolone, tacrolimus and IVIG was begun. Transcatheter arterial chemoembolization for HCC was also begun, and surgical treatment and proton beam therapy were considered but eventually ruled out because of the patient's poor liver function. Although complete restoration of muscle strength was not achieved, some therapeutic response was observed through immunosuppressive therapy, and the patient was able to be discharged.
A previous study reported that 1.6-3.0% of cases of adult myositis were positive for the anti-NXP-2 antibody [4], which is associated with calcinosis, s.c. oedema and dysphagia [1]. Moreover, adult patients with anti-NXP-2 antibody-positive DM are often associated with malignancies [3]. To the best of our knowledge, there are no reports of anti-NXP-2 antibodypositive DM associated with HCC. Although there are some reports of HCC-associated DM [5,6], they do not include anti-NXP-2 antibody-positive cases, and it is speculated that the limited availability of facilities capable of easily measuring the antibody is one contributing factor. The detection rate is lower for this antibody than for the anti-TIF1-gamma antibody, which is frequently detected in cases of cancerassociated DM [7]. Nonetheless, whenever a patient presents with cancer-associated DM, testing for anti-NXP-2 antibody should be done if possible. Conversely, if an adult patient has DM with anti-NXP-2 antibody positivity, an examination for malignancies is necessary.
DM associated with HCC is rare [8], and many patients with this condition die <1 year after DM diagnosis [5]. Large tumours are often found in cases of DM associated with HCC and are believed to affect the prognosis. Large HCC lesions often accompany reduced liver function, making it less amenable to surgical resection or radiation therapy and therefore more strongly associated with a poor prognosis. In the present case as well, curative treatment for the HCC was challenging.

Data availability
Derived data supporting the findings of this case report are available from the corresponding author on request.

Funding
No specific funding was received from any bodies in the public, commercial or not-for-profit sectors to carry out the work described in this article.  Letter to the Editor