08 August 2022: Articles
A 73-Year-Old Man with an Incidental Diagnosis of Deltoid Intramuscular Myxoma Following a History of Trauma
Challenging differential diagnosis, Rare disease, Educational Purpose (only if useful for a systematic review or synthesis), Rare coexistence of disease or pathologyChristian Akem Dimala1ABCDEF*, Ibiyemi Oke1AEF, Fikru Merechi2BDE, Ryan P. Zimmerman13ABDEF
Am J Case Rep 2022; 23:e936654
BACKGROUND: Intramuscular myxomas are rare and benign soft-tissue tumors of uncertain differentiation. Predisposing or precipitating factors have not yet been reported. Activating mutation in GNAS (exons 8 and 9) is detected in >90% of sporadic cases. The role of chronic myopathy, tendinopathy, or trauma to muscles in the etiology of these neoplasms is not known. We report an unusual case of a deltoid mass found following longstanding rotator cuff tendinopathy and a recent fall, later confirmed to be an intramuscular myxoma on biopsy.
CASE REPORT: A 73-year-old man with a 5-year history of left shoulder pain and rotator cuff tear presented with intractable pain in his left shoulder after a recent fall at home. Physical examination was suggestive of a rotator cuff injury and magnetic resonance imaging (MRI) of the left shoulder revealed a 2.7×2.5×3.7cm T1 hypo- and T2 hyperintense oblong mass-like signal abnormality with heterogeneous, predominantly peripheral enhancement within the deltoid muscle concerning for a malignant mass. Surgical resection was carried out along with left reverse total shoulder replacement, and histopathology revealed findings consistent with an intramuscular myxoma.
CONCLUSIONS: Intramuscular myxomas are rare, benign tumors. This case report presents one such myxoma incidentally found in a patient with longstanding rotator cuff tendinopathy and a recent fall. Although this co-occurrence is likely incidental, further research and case series review of similar presentations may influence postulations of the pathophysiology of myxomas.
Keywords: Tendinopathy, Myxoma, Neoplasms
Intramuscular myxomas are rare, benign soft-tissue tumors of uncertain differentiation [1,2]. These painless masses predominantly occur in the large skeletal muscles, especially of the thighs and less commonly in the buttocks, calves, neck, and shoulders [2,4]. Myxoma occurrence in the deltoid muscle is even rarer; fewer than 10% of all intramuscular myxomas occur in the upper arm . These neoplasms comprise stellate cells with thin collagen and mucinous stroma [2,4,5]. There are no known predisposing or precipitating factors reported to date, but activating mutation in GNAS (exons 8 and 9) is detected in most sporadic cases . Intramuscular myxomas have been reported in patients who presented with pain in the affected muscle after trauma or a fall . It is, however, not known if chronic myopathy, tendinopathy, or trauma to muscles predispose to intramuscular myxomas formation. We report an unusual case of a deltoid mass in a patient with longstanding rotator cuff tendinopathy and a recent fall, later found to be an intramuscular myxoma on biopsy.
A 73-year-old man with a history of paroxysmal kinesigenic dyskinesia, cervical and lumbar neural foraminal stenosis with multiple prior back surgeries, and a 5-year history of left shoulder pain and rotator cuff tear presented with intractable pain in his left shoulder after a recent fall at home.
He had previously consulted at other facilities for this longstanding left shoulder pain and had multiple imaging studies of his left shoulder (Figure 1) and had received steroid injections with little improvement in his symptoms. A magnetic resonance imaging (MRI) scan of his left shoulder 7 years prior to his current presentation showed diffuse tendinosis within the supraspinatus tendon and anterior infraspinatus tendon with associated articular surface partial rotator cuff tear, while another MRI scan of his left shoulder done 5 years prior to the current presentation reported a rotator cuff tear of the infra-and supraspinatus tendons with fatty infiltration and normal subscapularis. Ultrasound imaging of his left shoulder 4 years prior to the current presentation reported a well-marginated hypoechoic 23×32×21 mm collection in the anterior left deltoid, likely a hematoma (Figure 2), after he presented with pain and a palpable mass in his left shoulder. A final MRI of his left shoulder 3 months prior to the current presentation showed severe tendinopathy of the rotator cuff muscle tendons (Figure 3).
At his current presentation to our facility, he also reported back pain and a tingling sensation down his left arm. On examination, he had positive glenohumeral crepitus, tenderness along the joint lines anteriorly and posteriorly, and pain with left shoulder motion. Impingement signs I and II, drop arm test, and Speed’s test were positive. A left shoulder X-ray showed severe glenohumeral joint arthritis with 75% superior humeral head subluxation and flattening of the humeral head, but there was no fracture. MRI of the left shoulder this time revealed a 2.7×2.5×3.7cm T1 hypo- and T2 hyperintense oblong mass-like signal abnormality, demonstrating heterogeneous predominantly peripheral enhancement within the inferior deltoid muscle (Figure 4). Other abnormalities noted on MRI were degenerative changes of the shoulder with a complete full-thickness tear of the supraspinatus tendon with retraction of the proximal head (Figure 4).
Following orthopedic assessment, his rotator cuff tear was not repairable, and given his severe glenohumeral degenerative changes, he had left reverse total shoulder replacement and excision of the left upper arm mass. Histopathology of the mass revealed a hypocellular lesion with bland nuclei in a background of abundant extracellular myxoid stroma, consistent with an intramuscular myxoma (Figure 5). He had remarkable improvement in his shoulder pain after surgery and progressive improvement of his left shoulder range of movement with physical therapy. At one-year follow up, he regained nearly full range of motion of his left shoulder and there was no evidence of recurrence of the myxoma.
Intramuscular myxomas are rare benign tumors with an incidence of 1 case per million population and a female preponderance [3,7]. These neoplasms of uncertain differentiation present histologically as stellate cells within a myxoid/ mucinous stroma [1,3,8,9]. Intramuscular myxomas predominantly occur in large skeletal muscles of the thighs but less so in the buttocks, calves, shoulders, cervical region, and para-spinal muscles of the back . We found fewer than a dozen published cases of intramuscular myxomas of the deltoid muscle [10–16]. They usually present as asymptomatic slowly enlarging masses incidentally found on imaging studies but can also present with pain depending on the extent of compression of adjacent structures.
Activating mutation in GNAS (exons 8 and 9) is detected in most sporadic cases  and no precipitating factors have been reported in the literature. Although this unusual occurrence of a myxoma after a fall as observed in our patient and a prior case report  is likely coincidental, the role of trauma in the pathophysiology of these neoplasms should be questioned. Likewise, the observed chronic rotator cuff tendinopathy in our patient raises the question of the role of chronic myopathy and tendinopathy in the pathophysiology of these tumors due to persistent muscle destruction and remodeling over time.
Diagnosing intramuscular myxomas with imaging presents some challenges given their rarity . Intramuscular myxomas typically present as well-defined ovoid heterogenous hypoechoic masses with some internal echoes and absent internal vascularity on ultrasound [2,17]. MRI usually demonstrates a homogenous mass with low to intermediate signal intensity relative to surrounding muscle on T1-weighted images or a high signal intensity on T2-weighted images [5,7,17,18]. CT scans typically show a well-defined homogenous soft-tissue mass with lower attenuation compared to surrounding muscle . Despite these typical presentations of myxomas on various imaging modalities, it is not unusual for them to be mistaken for other mesenchymal lesions such as lipomatous lesions , highlighting the importance of biopsy and/or resection for histo-pathology studies to ultimately make a diagnosis.
Intramuscular myxomas are generally benign and although early diagnosis of these neoplasms does not improve survival, it can significantly improve quality of life when diagnosed promptly and resected, especially in patients presenting with symptoms such as intractable pain due to compression of adjacent structures.
Intramuscular myxomas are rare, benign tumors. This case presents one such myxoma incidentally found in a patient with longstanding rotator cuff tendinopathy and a recent fall. Although this co-occurrence is likely incidental, further research and case series review of similar presentations may influence postulations of the pathophysiology of myxomas.
FiguresFigure 1.. Flow diagram showing the various radiographic studies of the left shoulder performed prior to current presentation. ACJ – acromioclavicular joint; IS – infraspinatus; MRI – magnetic resonance imaging; SC – subscapularis; SS – supraspinatus. Figure 2.. Ultrasound of the left shoulder showing a hypoechoic 23×32×21 mm collection in the left anterior deltoid area. Hematoma indicated by asterisk *. Figure 3.. Magnetic resonance imaging with i.v. gadolinium contrast images of the left shoulder showing severe tendinopathy of the rotator cuff muscles. (A) Coronal T2 with fat suppression image (* acromion, ~ deltoid tendon, × humeral head, + supraspinatus tendon). (B) Axial PD with fat suppression (* infraspinatus tendon, + subscapularis, ~ deltoid tendon, × humeral head). There is a full-thickness complete tear of the supraspinatus tendon with retraction of the majority of the tendon to the superior humeral head proximally 2.5 cm from the insertion. The tear extends into the anterior aspect of the infraspinatus tendon, involving approximately 50% of the infraspinatus tendon with sparing of the posterior fibers. The teres minor tendon is intact, without significant tendinopathy. There is fatty atrophy of the supraspinatus and infraspinatus muscle bellies and severe osteoarthritis of the acromioclavicular joint. Figure 4.. Magnetic resonance imaging with i.v. gadolinium contrast images of the left shoulder showing a 2.7×2.5×3.7 cm oblong mass with the inferior deltoid muscle. (A) Coronal T2 with fat suppression image (* intramuscular mass, ~ deltoid tendon, × humeral head). (B) Axial PD with fat suppression (* intramuscular mass, ~ deltoid tendon, × humeral head). Within the inferior deltoid muscle is an oblong mass-like signal abnormality which is T1 hypo- and T2 hyperintense, measuring approximately 2.7×2.5×3.7 cm. Post-gadolinium sequences demonstrate heterogeneous regions of predominantly peripheral enhancement. Figure 5.. Histopathology slides of biopsied left deltoid muscle mass. (A) Entrapped skeletal muscle fibers at the periphery of the tumor (lower half represents the skeletal muscle fibers which are splayed by the tumor cells). (B) The tumor is a hypocellular lesion composed of bland cells in a background of abundant extracellular myxoid stroma. (C) Small capillary-sized vessels are seen. Necrosis and mitotic figures are not identified. Uniform spindle-to-stellate-shaped cells with uniform oval nuclei and indistinct eosinophilic cytoplasm are noted.
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