Introduction

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children which is thought to be a high grade neoplasm originating from skeletal myoblast like cells. Two-thirds of patients are diagnosed before 6 years of age [1, 2]. Fewer than 25% of patients have overt distant metastasis at diagnosis typically in one site especially the lung. Other sites of metastasis include bone, bone marrow, omentum, and pleura [3]. RMS with bone marrow metastasis accounts for 6% of all RMSs, most commonly arising from the primary small tumors in the extremities [4]. Extremity tumors are common in adolescence which spread to regional lymph nodes and bone marrow; and when disseminated can mimic a hematologic malignancy [5, 6]. Here we report a 17-year-old patient with disseminated RMS at presentation masque ring lymphoproliferative diseases.

Case report

A 17-year old boy presented with complaints of progressive weight loss, fatigue and generalized bone pain during recent 2 months. He did not have any past medical or drug history. In the physical examination, he was an alert cachectic boy with good compliance. His vital sign was stable with low grade fever (Central temperature 38.3 °C), he had generalized lymphadenopathy in cervical, axillary and inguinal region and mild splenomegaly. The thoracolumbar vertebras were tender and his lower limb forces were decreased, as he could not hold a weight-bearing position. Due to initial poor performance status and generalized pain, complete neuromuscular physical examination could not be performed. Laboratory tests at admission showed anemia with hemoglobin (6 g/dL) and leukocytosis 17,000 with neutrophil predominance (80%), hypercalcemia (calcium: 16.2 mg/dL), increased LDH (1435UI/l) and creatinine (3.4 mg/dL). Parathormone level (11 pg/mL, normal 15–68 pg/mL) was suppressed. Other serum biochemistries were normal (Table 1). Peripheral blood smear did not reveal any abnormal cell or blast and bone marrow biopsy was necrotic and not diagnostic.

Table 1 Laboratory data at admission
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Vertebral MRI was done due to thoracolumbar tenderness and paraparesia which revealed diffuse marrow infiltration, collapse of several vertebral bodies in C4, T5, L4 with spinal and thecal compression (Fig. 1). CT scans of the thorax and abdominopelvic was performed without contrast because of the patient’s nephropathy and showed splenomegaly and lytic bone lesions without any soft tissue mass or extraosseous calcification.

Fig. 1
figure 1

A Cervicothorasic MRI revealed diffuse marrow infiltration, collapses in C4, T5 with thecal compression

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99mTc whole body bone scan was done and revealed wide spread bone metastases in central and peripheral skeleton. Soft tissue bone seeking radiotracer uptake in the lungs was also detected (Fig. 2).

Fig. 2
figure 2

Whole body blood pool scan with 99mTc-MDP showed significant soft tissue radiotracer uptake in the lungs bilaterally and stomach as well as gluteal muscles. Whole body delayed images showed heterogeneous increased radiotracer uptake throughout central and peripheral skeleton more severe in lumbar spine, pelvic bones and proximal femora. Also significant soft tissue uptake is noted in the lungs, low-grade soft tissue radiotracer uptake is detected in the stomach and gluteal muscles

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Inguinal lymph node biopsy revealed monomorphic cells with round nuclei and clear cytoplasm diffusely infiltrate lymph node; in favor of lymphoproliferative disorder. Immuno-histochemical study was performed, and the definite diagnosis was rhabdomyosarcoma, not otherwise specified (NOS); with diffuse staining of vimentin and positive staining with MyoD1 and desmin (Fig. 3). No molecular and gene fusion test was examined.

Fig. 3
figure 3

A diffuse infiltration of rather small cells with round nuclei and clear acidophilic cytoplasm, B presence of some rhabdoid cells with marginal nuclei and abundant acidophilic cytoplasm, C Immunohistochemical staining reveal positive staining for Desmin, and D Myogenin

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Intravenous saline hydration, pamidronate and calcitonin were given to treat hypercalcemia and eventually serum calcium level normalized (9.3 mg/dL) on the 6th day of treatment. The patient underwent urgent radiotherapy for vertebral fractures and myelopathy followed by chemotherapy with VAC regimen (vincristine 2 mg, doxorubicin 90 mg, cyclophosphamide 2 g) for 3 cycles. However, despite mild initial improvement, our patient died from progressive illness and sepsis three month later.

Discussion

Rhabdomyosarcoma is responsible for one half of soft tissue tumors of children and is more common under 6 years old [2]. The typical first presentation of RMS includes involvement of head and neck, genitourinary tract and extremities [7]. In our patient, we did not find the primary tumor site and his first clinical symptom was overt and multi-organ metastasis which is not common.

Constitutional symptoms, high level of LDH, bone marrow involvement with necrosis and superficial lymph node enlargement mimicked lymphoma/leukemia at presentation. This diffuse metastatic involvement in rhabdomyosarcoma is rare at diagnosis and fewer than 15 percent of patients have multiple metastatic sites initially. Also the primary pathological assessment of our patient was in favor of high grade lymphoma; it emphasizes the importance of immune-phenotyping before starting therapy in malignancies especially lymphoma [5, 6].

Our patient had severe hypercalcemia (16.2) secondary to diffuse lytic bone lesions; it reduced his kidney function (creatinine 3.4) and suppressed PTH level. In bone scan with 99mTc, soft tissue bone seeking radiotracer uptake in the lungs could be due to metastatic calcification secondary to elevated serum calcium or tumoral involvement (lymphangitis carcinomatosis); because in chest CT, no tumoral involvement was detected, hypercalcemia was the main cause of this finding in body bone scan. An Lu in 2016 reported a patient with metastatic carcinoma and hypercalcemia that had extra-osseous uptake in his lung and gastric area in bone scan [8].

Outcomes for patients with metastatic RMS are poor and long term event free survival is less than 20% [9]. The standard recommendation for these group of patients is chemotherapy based on VAC regimen [10]. We initially stabilized our patient’s general condition by hydration and lowering calcium level. Urgent radiotherapy was performed because of acute myelopathy. We started VAC chemotherapy regimen but eventually had to stop it because of toxicity and the patient’s poor performance status.

Conclusion

Metastatic RMS can mimic lymphoproliferative disorders at presentation. Clinicians must be aware of this diagnosis especially in young adults. Immune-phenotyping is important for definite diagnosis of these patients. Assessment of bone scan in patients with hypercalcemia may be different due to the possibility of extra-osseous calcifications.