Idiopathic inflammatory myopathy (IIM) consists of two distinct subtypes: dermatomyositis (DM) and polymyositis (PM) [1]. Since the first report of the association with gastric carcinoma by Stertz [2] in 1916, its relationship with malignant diseases has been well-recognized so far. Although both types of IIM have the increased risk of malignancy than general population, DM is known to have more likelihood of occurring malignant diseases than PM [3], and the types of malignancies are different from each other. DM is more likely to have nasopharyngeal cancer, while PM more likely have colorectal cancer, lung cancer, and hepatic cancer despite almost all types of malignancies could occur with IIM even in hematologic malignancies [4-7]. However, IIM related to pancreatic cancer was scarcely reported so far, especially in patients with PM. Therefore, we report herein a case of PM which was developed immediately after the diagnosis of ductal adenocarcinoma of the pancreas.

An 82-year-old female was referred to gastroenterology department complaining of abdominal discomfort, dyspepsia, and weight loss despite the treatment of outside local clinic. The patient had diabetes mellitus, hypertension and gastric adenoma which was treated by endoscopic mucosal resection one month ago. She did not have a family history of malignant diseases. Considering the patient’s age of more than 80 years, the diagnostic work-up of cancer was performed in addition to the routine tests. The results of laboratory tests were as follows: white blood cell count 9,670/mm³, hemoglobin 11.3 g/dl, platelet count 285,000/mm³, total bilirubin 3.66 mg/dl (range, 0–1.20 mg/dl), direct bilirubin 2.23 mg/dl (range, 0–0.30 mg/dl), alkaline phosphatase 706 U/L (range, 35–105 U/L), gamma glutamyl-transferase 901 U/L (range, 6–42 U/L), aspartate aminotransferase (AST) 63 U/L (range, 0–40 U/L), alanine aminotransferase (ALT) 34 U/L (range, 0–40 U/L), amylase 176 U/L (range 28–100 U/L), lipase 481 U/L (13–60 U/L); CA 19–9 1,572 U/ml (<27 U/ml). Hepatitis B surface antigen was negative and hepatitis B surface antibody was positive. Antibodies against the hepatitis C virus were negative. For the evaluation of gastrointestinal malignancies, upper endoscopy and abdominal computed tomography (CT) were conducted as well. Upper endoscopy showed mucosal nodularity with slight irregularity in the background of chronic atrophic gastritis, and it was diagnosed with a low-grade adenoma by forceps biopsy. Abdominal CT revealed about 3 cm sized hypodensity mass lesion on the pancreas head portion (Fig. 1). The pancreas mass caused to biliary obstruction with diffuse upstream bile duct dilation, abutting to superior mesenteric vein. Several enlarged lymph nodes were identified on several peripancreatic, periportal, and aortocaval areas. Therefore, percutaneous transhepatic biliary drainage (PTBD) was performed to decompress the biliary obstruction (Fig. 2). After the PTBD procedure, biliary obstruction as well as patient’s symptoms were relieved continuously.

Figure 1. Abdominal computed tomography image shows about 3 cm sized hypodensity mass on head portion of the pancreas. (A) Transverse view image, (B) coronal view image (arrows).

Figure 2. (A) Cholangiography via percutaneous tract shows diffuse bile duct dilation. (B) Percutaneous transhepatic biliary drainage for biliary decompression is completed.

Furthermore, she abruptly complained of the muscle weakness and difficulty on raising her both arms. However, her skin did not show any cutaneous eruptions, suggesting of DM. Neurological examination showed normal sensory function; however, she had III/II decrease of both upper arms on extensor and flexor compartments. Therefore, additional tests of muscle enzymes and electromyography (EMG) were performed for the evaluation of myositis, which revealed abnormal findings as follows: elevated creatine kinase (CK) 43,052 IU/L (<170 U/L), aldolase 127.2 U/L (1–7.6 U/L), lactate dehydrogenase (LDH) 1,918 IU/L (135–214 U/L), AST 1,092 IU/L, ALT 667 IU/L, ALP 356 U/L, erythrocyte sedimentation rate 61 mm/hr (25 mm/hr), and C-reactive protein 4.3 mg/dl (<0.5 mg/dl). Autoimmune markers were all negative for anti-nuclear antibody, anti-Jo-1 antibody, anti-Sm antibody, anti-Ro/La antibody, and anti-smooth muscle antibody. Nerve conduction study showed that all examined nerve parameters were within normal limits. However, EMG on biceps & pronator teres showed increased positive sharp waves, fibrillation potentials and polyphasic motor unit action potentials (MUP), suggesting myopathic MUPs and electromyographic myotonia. Magnetic resonance imaging of the both upper arms (T2-weighted images) revealed multiple high-intensity signals at muscle signal involving triceps muscle long head, brachialis muscle, bicep muscle, subscapularis, infraspinatus, teres major, deltoid post. belly, trapezius, pectoralis major (Fig. 3). A muscle biopsy was not performed because cancer-related myositis could be sufficiently presumed based on the clinical situations and test results. Thus, corticosteroids treatment with prednisone 1 mg/kg was initiated. During the steroid treatment, her symptoms started to improve, and the elevated values of CK and LDH decreased as well. After the resolving the symptoms of myositis, Endoscopic ultrasonography-guided fine needle aspiration was performed for the pancreas head lesion (Fig. 4), and the biopsy specimen finally showed ductal adenocarcinoma of the pancreas. Therefore, PM could be diagnosed in a patient with pancreas head cancer.

Figure 3. Magnetic resonance images show high-intensity signals. T2-weighted images with fat suppression for (A) right shoulder and for (B) left shoulder. T2-weighted images with start tau inversion recovery sequence (C) for right upper arm and (D) left upper arm.

Figure 4. (A) Endoscopic ultrasonography (EUS) shows hypoechoic mass with irregularity on the head of the pancreas. (B) EUS guided fine-needle aspiration biopsy is performed via trans-duodenal approach.

IIM consists of two distinct subcategories: DM and PM. Proximal muscle weakness and muscle inflammation at the proximal extremities are the characteristic features of IIM, in which inflammatory cells infiltrations are usually identified. The diagnostic criteria proposed by Bohan and Peter [1] in 1975 has been widely used, and it comprises of 5 components: 1) characteristic erythematous skin rash, 2) symmetric weakness on proximal muscles, 3) elevated muscle enzymes, especially for aldolase, CK, and LDH 4) myogenic abnormalities on EMG, and 5) evidence of muscle edema, degeneration, inflammatory cell infiltration and fibrosis.

The positive relationship between IIM and malignancy has been well recognized. Based on epidemiologic studies by Hill et al. [4] with pooled analysis of nationwide data from European countries, the standardized incidence ratio was reported to be 3.0 (95% CI, 2.5–3.6) in patients with DM and 1.3 (1.0–1.6) in patients with PM. Recently, a study from Taiwan by Hsu et al. [3], the incidence of malignancies after myositis were 5.55% in patients with DM, and 3.26% in those with PM, revealing that the cumulative incidence of malignancies were significantly higher in patients with DM than in those with PM. Furthermore, based on the study by Liu et al. [8], the temporal association between the diagnoses of malignancy and DM was as follows; in about 70% of the DM patients, malignancy was detected within 1 year before or after DM diagnosis, and about 28% were diagnosed with malignancy at the time of the DM diagnosis.

When it comes to the types of malignancies, a study by Hsu et al. [3] showed that nasopharyngeal cancer, lung, and breast cancers were the most frequent types in patients with DM, whereas colorectal, lung and hepatic malignancies were in patients with PM. Meanwhile, IIM related to pancreatic cancer was scarcely reported especially in patients with PM although there are a few reports in patients with DM [4,9]. As shown in this case report, when sudden muscle weakness occurs in patients with underlying malignancies, PM should be considered as a differential diagnosis for the unexplained myopathy, even in the patients with pancreatic cancer. The pathophysiology of this relationship between IIM and malignancies are remains unclear, but abnormal autoantibodies by immunological dysfunction or paraneoplastic syndrome caused by malignant lesions are suggested as an underlying mechanism [10]. Regarding the treatment of IIM, corticosteroids is the agents of first choice, typically starting at a daily dose of 1.5 mg/kg [11]. In refractory or severe cases, intravenous immunoglobulin is an additional choice of treatment [12]. Methotrexate and azathioprine also can be used for common steroid-sparing agents. For the patients with malignancy related IIM, the malignancy needs to be treated or resected in order to improve the myositis although the cancer treatment does not guarantee the remission of myositis [9,13].

Because of the similarity of clinical features between DM and PM, it is difficult to make a definite diagnosis without muscle biopsies especially when the characteristic skin eruptions do not be manifested. Thus, muscle biopsy is a critical method for the differential diagnosis for the unexplained myositis. DM show the infiltrations of β cells and CD4⁺ T cells in the perimysial and perivascular area, which supports a humoral-medicated pathogenesis, whereas PM shows mononuclear macrophages cells and cytotoxic CD8⁺ T cells, which suggest a cell mediated cytotoxic mechanism [14]. Regarding the imaging techniques, MRI has several advantages than other imaging modalities because it can show high resolution images with multiple section planes with high sensitivity and specificity [15]. Furthermore, it can be performed non-invasively. T2WI on MRI exhibit hyperintensity signals of the area of inflammatory muscle edema. Additionally, two useful techniques are fat suppression and start tau inversion recovery sequence, which help eliminate fat signal that could interferes with the myositis-related inflammatory changes on T2WI findings [16].

In conclusion, for the patients with unexplained myopathy, IIM should be considered as a differential diagnosis, and it should be evaluated whether there is underlying gastrointestinal malignancies because IIM can occur in relation to various malignant conditions.

None

No potential conflict of interest relevant to this article was reported.