Two case reports of intra-articular nodular fasciitis of the knee confirmed by MYH9-USP6 gene fusion expression

Intra-Articular Nodular Fasciitis of the Knee, A Rare Clinical Presentation and Histological Diagnosis: A Case Report

Introduction

Nodular fasciitis is a rare, benign soft tissue lesion that can prove to be difficult to diagnose, especially when intra-articular.

Case presentation

A 17-year-old female softball player presents with several year history of right knee pain and swelling initially attributed to patellar maltracking refractory to non-operative and operative management.

Management and Outcomes

Initial pathology suggested tenosynovial giant cell tumor; however, further tissue diagnosis revealed nodular fasciitis, which was eventually resected.

Conclusion

Intra-articular nodular fasciitis of the knee is rare and may easily be misdiagnosed due to its nonspecific clinical presentation. Careful histological examination can aid in diagnosis. Nodular fasciitis should be considered in the differential diagnoses for intra-articular lesions of the knee joint.

Late-Onset Type 1 Diabetes Mellitus and Unexplained Subcutaneous Lesions

Nodular fasciitis is considered a reactive lesion of connective tissue originating from the proliferation of fibroblasts and myofibroblasts. Nodular fasciitis preponderantly localizes within the higher extremities, trunk, head, and neck. We are presenting a report on the case of a 38-year-old Navy pilot who developed nodular lesions in the area of the sternum and upper back and was diagnosed concomitantly with insulin-dependent diabetes mellitus (type 1 diabetes). The patient was treated for diabetic ketoacidosis using intensive insulin therapy protocol, and the nodules were surgically excised. He was discharged from the hospital four weeks later. In our presentation, we intend to highlight the essential characteristics of this rare lesion through a review of the literature and to identify an attainable link between the development of type 1 diabetes and nodular fasciitis.

An update on selected cutaneous (myo) fibroblastic mesenchymal tumors

Cutaneous (myo)fibroblastic tumors constitute a group of tumors with overlapping clinicopathological features and variable biologic behavior. In the present review we focus on the histomorphology, immunohistochemical profile and molecular background of the following entities: dermatofibrosarcoma protuberans (DFSP), CD34-positive fibroblastic tumor (SCD34FT), myxoinflammatory sarcoma (MIFS), low-grade myofibroblastic sarcoma, solitary fibrous tumor and nodular fasciitis. Although some of these entities typically arise in deep-seated locations, they may occasionally present as cutaneous/superficial tumors and might be challenging to recognize. This review covers in depth the latest advances in molecular diagnostics and immunohistochemical markers that have significantly facilitated the correct classification and diagnosis of these neoplasms.

A case report of an unusual temporomandibular joint mass: Nodular fasciitis

Nodular fasciitis (NF) is a benign myofibroblastic proliferation that grows very rapidly, mimicking a sarcoma on imaging. It is treated by local excision, and recurrence has been reported in only a few cases, even when excised incompletely. The most prevalent diagnoses of temporomandibular joint (TMJ) masses include synovial chondromatosis, pigmented villonodular synovitis, and sarcomas. Cases of NF in the TMJ are extremely rare, and only 3 cases have been reported to date. Due to its destructive features and rarity, NF has often been misdiagnosed as a more aggressive lesion, which could expose patients to unnecessary and invasive treatment approaches beyond repair. This report presents a case of NF in the TMJ, focusing on various imaging features, along with a literature review aiming to determine the hallmark features of NF in the TMJ and highlight the diagnostic challenges.

Cellular Fibroma of Tendon Sheath With Novel TNC-USP6 Gene Fusion Clinically Mimicking Arthritis in a 7-Year-Old Boy

Cellular fibroma of tendon sheath (CFTS) is a rare, benign myofibroblastic neoplasm of tenosynovial soft tissues closely resembling nodular fasciitis (NF), but is histomorphologically distinct from classic fibroma of tendon sheath (FTS). We report a case of a pediatric patient with thumb swelling clinically concerning for arthritis with a biopsy demonstrating myofibroblastic proliferation with features consistent with NF/CFTS, and molecular studies confirming the presence of a USP6 gene fusion (TNC-USP6). This case highlights a unique clinical presentation of CFTS in a pediatric patient mimicking an inflammatory or reactive/non-neoplastic musculoskeletal disorder and the increasingly crucial role of molecular testing to differentiate a reactive myofibroblastic process from a neoplasm. Moreover, this report identifies TNC as a new fusion partner to USP6 fusion partner adding to our growing understanding of the USP6-rearranged family of tumors.

Intraarticular nodular fasciitis-detection of USP6 gene fusions in three cases by targeted RNA sequencing

Intraarticular nodular fasciitis arising in the joint synovium is an uncommon lesion. Most cases have been reported in the knee and rarely in other joints. A USP6 gene fusion has so far been documented in only four cases of intraarticular nodular fasciitis, three were located in the knee and one in the proximal interphalangeal joint. In all three cases located in the knee, MYH9 was detected as a USP6 fusion partner. We analysed three cases of intraarticular nodular fasciitis for the presence of USP6 fusion by targeted RNA sequencing. Two cases were located in the hip (a 25-year-old female and 48-year-old male) and one in the shoulder (a 38-year-old male). We detected a MYH9-USP6 fusion in the two hip cases and a COL1A1-USP6 fusion in the shoulder case. Our findings provide additional evidence that intraarticular nodular fasciitis is a form of nodular fasciitis arising in the joint synovium, harbouring a USP6 fusion. Although a MYH9-USP6 fusion seems to predominate in intraarticular nodular fasciitis, other fusion partners of the USP6 gene may also be involved. Detection of a USP6 fusion by targeted RNA sequencing may assist in confirming the diagnosis in selected cases.

Nodular fasciitis: a comprehensive, time-correlated investigation of 17 cases

The self-limited nature of nodular fasciitis (NF) is well-known but its precise mechanism has not yet been clarified. We observed that "young" NF (preoperative duration <1 month) consistently contains a higher percentage (~80%) of USP6 break-apart FISH signals than "old" NF (preoperative duration >3 months) (~20%). Thus, we hypothesized that our original observation may reflect a connection with the self-limited nature of NF. Seventeen cases with reliable data concerning the onset were selected, thus approximating the lifetime of each tumor. Besides the USP6 interphase FISH examination, we also checked the most common MYH9-USP6 fusion using RT-PCR. Because of the known pathways of the tumorigenesis of NF, the mRNA level of USP6, TRAIL, IFN-beta, JAK1, STAT1, STAT3, JUN, and CDKN2A was measured using qRT-PCR. Regarding proteins, USP6, p16, p27, TRAIL, and IFN-beta were examined using immunohistochemistry. Targeted gene panel next-generation sequencing (NGS) of three cases was additionally performed. We found a strong negative correlation (p = 0.000) between the lifetime and percentage of USP6 break-apart signals and a strong positive relationship (p = 0.000) between USP6 break-apart signals and mitotic counts. Results of immunostainings, along with qRT-PCR results, favored the previously-suggested USP6-induced negative feedback mechanism through activation of TRAIL and IFN-beta, likely resulting in apoptosis and senescence of tumor cells harboring USP6 fusions. Targeted-NGS resulted in the detection of several variants, but no additional recurrent changes in the pathogenesis of these tumors. We revealed on a cellular level the USP6-induced negative feedback mechanism. In conclusion, we emphasize that in "old" NF, the percentage of USP6 break-apart FISH signals can be as low as 14-27% which can be very important from a differential diagnostic point of view. We emphasize that a careful examination and interpretation of the NGS data is needed before clinical decision-making on treatment.

USP6-Associated Neoplasms: A Rapidly Expanding Family of Lesions

Nearly 20 years ago, the first description of a translocation involving chromosome 17 on which USP6 resides was described. Since then, not only the culprit gene but also many fusion partners, leading to transcriptional activation of USP6, have been detected. The first neoplasm known to harbor USP6 rearrangements was aneurysmal bone cyst. Since then, other entities like nodular fasciitis, myositis ossificans, fibro-osseous pseudotumor of digits, and a subgroup of fibromas of tendon sheath, probably representing tenosynovial nodular fasciitis, have been added to the list of USP6-rearranged lesions. Remarkably, all of them share clinical as well as morphological characteristics, and authors have suggested that these entities actually belong to the same spectrum. This review summarizes the current knowledge regarding USP6-rearranged lesions and further elaborates on how these neoplasms relate to one another. We propose to call these lesions UAN (Usp6-associated neoplasm).

Current Approaches for Personalized Therapy of Soft Tissue Sarcomas

Soft tissue sarcomas (STS) are a highly heterogeneous group of cancers of mesenchymal origin with diverse morphologies and clinical behaviors. While surgical resection is the standard treatment for primary STS, advanced and metastatic STS patients are not eligible for surgery. Systemic treatments, including standard chemotherapy and newer chemical agents, still play the most relevant role in the management of the disease. Discovery of specific genetic alterations in distinct STS subtypes allowed better understanding of mechanisms driving their pathogenesis and treatment optimization. This review focuses on the available targeted drugs or drug combinations based on genetic aberration involved in STS development including chromosomal translocations, oncogenic mutations, gene amplifications, and their perspectives in STS treatment. Furthermore, in this review, we discuss the possible use of chemotherapy sensitivity and resistance assays (CSRA) for the adjustment of treatment for individual patients. In summary, current trends in personalized management of advanced and metastatic STS are based on combination of both genetic testing and CSRA.

Intraarticular Nodular Fasciitis of the Knee With MHY9-USP6 Fusion: A Case Report

Background. Nodular fasciitis (NF) is a self-limiting, benign mesenchymal neoplasm of fibroblastic/myofibroblastic origin. Due to the fast growth, cellularity, and frequently observed high mitotic count, it is commonly misdiagnosed as a sarcoma, often resulting in overtreatment. Intraarticular examples of NF are extremely rare. Radiologically, NF can mimic fibroma of the tendon sheath, tenosynovial giant cell tumor, and synovial chondromatosis. Histology can vary from hypercellular, mitotically active lesions to fibrotic, less cellular ones, and can, therefore, mimic other benign and low-grade malignant neoplasms. Recently, the MYH9-USP6 fusion has been found in up to 92% of NF. Case Presentation. In this article, we report a case of a 38-year-old patient with an intraarticular lesion, radiologically suspicious of tenosynovial giant cell tumor. Histology demonstrated a spindle cell lesion composed of fibroblasts/myofibroblasts embedded in a highly collagenous/hyalinized stroma, partly arranged in short fascicles. Extravasated erythrocytes and rare mitotic figures were present. Immunohistochemically, tumor cells expressed smooth muscle actin and were negative for desmin, β-catenin, CD34, and SOX10. These findings rendered the diagnosis of NF. Molecular analysis using next-generation sequencing (Archer FusionPlex Sarcoma Panel) revealed gene rearrangement involving USP6 and MYH9 supporting the diagnosis of NF in the knee joint. Conclusions. Radiological and histological features of NF can overlap with other benign and low-grade malignant lesion. Identification of the USP6 gene rearrangements or finding of the MYH9-USP6 fusion, especially in core needle biopsies and in the lesions occurring at unusual sites, can result in adequate therapeutic approach avoiding overtreatment.

A case of intra-articular fasciitis in the elbow joint

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Intra-nodular fasciitis is very rare and there are only two reported cases of intra-articular nodular fasciitis in the elbow joint.

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It is difficult to diagnose preoperatively, so a clear diagnosis can be obtained only after excisional biopsy.

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As local recurrence has not occurred in previously reported cases, we think that arthroscopic resection is suitable for treatment of this disease.

Introduction

Nodular fasciitis is a benign myofibroblastic proliferation arising from the fascia. Until now, there have been only two reported cases of intra-articular nodular fasciitis in the elbow joint.

Presentation of case

We report a case of a 19-year-old woman with a 3-month history of pain in the left elbow. Contrast-enhanced T1-weighted magnetic resonance imaging (MRI) showed an intra-articular lobulated mass on the anterior portion of the elbow joint, with accompanying effusion. The patient subsequently underwent arthroscopic excision of the mass. Histologically, intra-articular nodular fasciitis was the final diagnosis. At the most recent follow-up, 20 months after surgery, the patient had no subjective symptoms, including pain. The final MRI findings showed no tumor recurrence.

Discussion

As nodular fasciitis is not generally known to arise within a joint, the occurrence at such anatomical locations may lead to a misdiagnosis. Intra-articular nodular fasciitis is rarely encountered, and therefore, is not usually considered during the clinical investigation of joint symptoms.

Conclusion

Preoperative diagnosis was difficult in this case because of nonspecific preoperative clinical findings. Although histological examination is necessary to establish a diagnosis, we recommend that intra-articular nodular fasciitis should be included in the differential diagnosis of intra-articular mass lesions.