GS is a localized tumor formed by primitive myeloid cells at an extramedullary site. GS was first described by Burns in 1811 and named chloroma in 1853 due to the infrequent greenish appearance observed as a result of myeloperoxydase granules in the malignant myeloid cells (5
). GS may involve any organ system, including the skin, bone, soft tissues and lymph nodes. Spinal GS is extremely rare. It has been reported that the prevalence of GS in the spine is 1.0% among all patients with myeloid leukemia (7
). GS in the absence of clinically detectable leukemia is not common and only a few cases of GS in patients without leukemia have been observed with spinal involvement (8
). Among these, CNS involvement has been reported in 19% of non-leukemic GS patients (10
Pathologically, the variable morphology may be misleading in GS. The correct diagnosis is sometimes challenging and is obtained in only ~50% of non-leukemic patients due to the histological and radiological similarities to malignant lymphoma (11
). The definitive diagnosis of GS requires positive immunostaining for at least 1 of the myeloid associated antigens (CD68, MPO, CD43, CD45, CD117, CD99, CD33, CD34 and CD13), as well as negative staining for the lymphoid lineages CD3 and CD20 (2
). Bone marrow sampling is also necessary for the diagnosis of GS to assess the absence of AML. In the present case, immunohistochemical studies showed positivity for MPO and Ki67 and partly positive results for TdT, but negative results for CD20, CD79a, CD138, CD15, CD5 and CD3, indicating GS. The immunohistochemical findings were compatible with a monoblastic or myelomonoblastic variant of myeloid sarcoma. In addition, bone marrow aspiration showed a normal result, indicating no involvement of the bone marrow.
An early and precise diagnosis of spinal GS with MRI evaluation facilitates appropriate treatment with further therapy (7
). However, MRI is unable to evaluate the metabolism. FDG-PET is reported to be more sensitive for the detection of malignant tumors with increased glucose metabolism (13
). In the present case, FDG-PET was used to estimate the malignancy of the tumor and the treatment efficacy. It was observed that FDG-PET successfully identified the active lesion and demonstrated the malignancy. A decrease in FDG uptake was observed 2 months after treatment. The follow-up FDG-PET suggested that adequate treatment contributed to the reduction in the cellularity of the tumor.
The prognosis of patients with GS depends on the initial context in which it occurs. Out of all isolated GS patients, 66–88% develop AML within 9–11 months of diagnosis (3
). In the present case, the patient developed CNSL 2 months after the diagnosis of GS. The optimal treatment for GS has not been fully established, partially due to the variety of clinical presentations. Chemotherapy, radiation therapy, bone marrow transplantation, surgical resection or a combination of approaches are employed in various cases. Surgery is generally reserved for patients with acute spinal cord compression or neurological symptoms. However, surgery is not always required and may worsen the prognosis due to the delayed administration of induction chemotherapy. Treating GS in the same manner as AML, even in the absence of clinically detectable leukemia has been previously reported (8
). Combination treatment with radiotherapy and chemotherapy resulted in improved survival (3
). However, isolated CNS GS and meningeal myeloid leukemia may be successfully treated without radiotherapy (16
In accordance with the previously mentioned studies, the present patient was successfully treated using surgery and intensive anti-leukemic chemotherapy accompanied by intrathecal injections. The present case highlighted the importance of a correct diagnosis. Pre-therapeutic examinations should be the basis for the diagnosis of a mass with an atypical clinical presentation. Notably, treating GS in the same manner as AML may benefit patients with isolated spinal GS.