Role of Positron Emission Tomography-computed Tomography in a Case of Suspected Paraneoplastic Inflammatory Polymyositis with Urinary Bladder Tumor

Introduction

PET-CT is a useful modality in the imaging and subsequent treatment planning of patients with cancer. Not only is it useful in staging, response evaluation and restaging but also has a significant role in initial detection and evaluation of cancers. Paraneoplastic syndromes are one such indications where PET-CT plays an important role for detection of primary malignant lesion.

Case Report

A 50-year-old male patient was admitted to the hospital with complaints of myalgias of the upper and lower limb muscles for about 2–3 months and progressive difficulty in rising from a chair, walking, and combing hair. There was no fever, arthralgias, paraesthesias, skin lesions, rash, shortness of breath, cough, abdominal pain, or other symptoms. His physical examination was also unremarkable except for reduced muscle strength (3/5). Laboratory investigations showed elevated plasma creatine kinase (CK). Anti-nuclear antibodies were negative. A magnetic resonance imaging (MRI) of the upper and lower limb muscles was performed and revealed an increase in bulk with increased signal intensity on T2 sequencing of multiple upper and lower limb muscles with sparing of the posterior compartment muscles of the lower limb, suggestive of acute myositis. Electroneuromyography (ENMG) showed features consistent with myoneuropathy. As inflammatory polymyositis (PM) is a well-known paraneoplastic syndrome (PNS), screening positron emission tomography-computed tomography (PET-CT) was done at our center which showed focal areas of heterogeneous attenuation and mild diffuse 18F-fluorodeoxyglucose (18F-FDG) tracer uptake in the upper limb muscles and medial, anterior, and lateral compartment muscles of both lower limbs [Figure 1]. In addition to the muscle findings, PET/CT showed a 18F-FDG avid (maximum SUV 11.7) irregular lobulated heterogeneously enhancing mass arising from the dome of urinary bladder with intraluminal polypoid and extraluminal exophytic soft tissue component [Figures 2 and 3]. Biopsy of the bladder mass revealed small cell cancer.

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Figure 1 Maximum intensity projection image showing mild diffuse fluorodeoxyglucose uptake in upper limb, chest wall and lower limb muscles

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Figure 2 Positron emission tomography-computed tomography axial images showing urinary bladder mass and left external iliac lymph node metastasis; also seen is mild diffuse uptake in pelvic muscles

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Figure 3 Positron emission tomography-computed tomography coronal images showing urinary bladder mass arising from dome with left external iliac lymph node metastasis

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Discussion

PNS occurs in many types of cancers. SCLC is the most common cancer with PNS in adults and Neuroblastoma in children. Paraneoplastic lesions can involve any part of the nervous system, such as brain, spinal cord, peripheral nerves, nerve-muscle joints, and muscles, therefore PNS present a variety of neurological symptoms. Inflammatory PM is a well-known paraneoplastic symptom. It has a prevalence rate estimated at approximately one per 100,000 in the general population. There is a female to male predominance of about 2:1. The peak incidence in adults occurs between the ages of 40 and 50, but individuals of any age may be affected.[1]

The major clinical manifestation of these inflammatory myopathies is muscle weakness. In addition, patients with dermatomyositis (DM) have characteristic skin lesions. Muscle weakness is generally symmetric and predominantly proximal.[2] Elevations in serum CK, lactate dehydrogenase, aldolase, and aminotransferases occur in most patients. Autoantibodies are found in a majority of patients. Electromyography findings are helpful in confirming the presence of a myopathic process and in indicating which muscle groups are most involved. Histologic features of inflammatory PM include muscle fiber necrosis, degeneration and regeneration, and inflammatory cell infiltration. Cellular infiltrates are located predominantly within the fascicle, consisting of cytotoxic CD8+ T-cells and macrophages.[3]

Perhaps, the most robust data describing the link between myositis and malignancy were published by Hill et al.[4] in 2001. The authors identified 618 DM and 914 PM patients. Cancer was detected in approximately 30% of DM and 15% of PM patients, with over 60% of tumors diagnosed after the diagnosis of myopathy. Both groups were noted to have increased cancer risks compared with the general population (standardized incidence ratio of 3.0 for DM, 1.4 for PM). Other studies have reported a frequency of malignancy of 15%–25%.[5]

The spectrum of malignancies associated with DM or PM parallels the distribution in the general population with the possible exceptions of an increased frequency of cervical, lung, ovarian, pancreatic, bladder, and gastric carcinomas, and with non-Hodgkin lymphoma. Cancer can be diagnosed before, at the time of, or after the diagnosis of myositis with a peak incidence occurring within the 2 years period before and after the development of myositis.[6] Furthermore, in some patients, the myositis is first diagnosed at a time of recurrence of a previously diagnosed cancer, whereas in others, the myositis reactivates at a time when cancer first becomes obvious.[7]

Our patient was suspected as having PM based on clinical presentation, elevated serum CK, MRI, and ENMG. As part of the further evaluation of PM as PNS, PET/CT was performed at our center. PET/CT showed a 18F-FDG avid (maximum SUV 11.7) irregular lobulated heterogeneously enhancing mass araising from the dome of the urinary bladder with intraluminal polypoid and extraluminal exophytic soft tissue component. Biopsy of the bladder mass revealed small cell cancer.

Small cell carcinoma of the urinary bladder (SCBC) is a rare type of malignant tumor of the urinary tract with a mean frequency of 0.7% and range between 0.35% and 1.8%. The reported incidence is <1–9/1,000,000 habitant. Since 1980, <1000 cases of SCCB have been diagnosed and reported in the literature up to July 2011. The demographic characteristics of SCCB are similar to those seen in patients with transitional cell carcinoma (TCC). The majority of patients are male, with a mean sex ratio equal to 5:1, and range between 1:1–16:1.[8] As it does not have specific symptoms and its epidemiological features are similar to TCC of the bladder, it is often misdiagnosed. The disease generally occurs in older males; the majority of patients develop painless gross hematuria (90%) and a few exhibit symptoms of bladder irritation. Histologically, small cell carcinomas of the bladder are identical to small cell carcinomas of the lung. Comprehensive therapy that combines surgery, radiotherapy and chemotherapy is the main method of treatment. Due to the low incidence of SCBC, there are no clinical data-based prospective case-control studies; therefore, more experience is necessary to analyze the best treatment plan.

Summary

PET/CT is valuable to identify or exclude an occult malignancy in patients with suspected PNSs. It is a highly sensitive and specific imaging technique for identification of occult malignancies. It is useful not only in the diagnosis but also in the therapy assessment and follow up of these patients.