Introduction

Myeloid sarcoma (MS) or granulocytic sarcomas is an extramedullary proliferation of myeloblasts or immature myeloid cells. It is usually associated with acute myelogenous leukemia (AML) occurring in approximately 3% of these patients [1]. It can also occur in patients with chronic myelogenous leukemia (CML), reflecting the onset of accelerated phase.

It can affect the skin, the bone, the soft tissue of the head and neck, the lymph nodes, and rarely the spine [2]. Epidural involvement is even scarce, occurring in 0.2% of patients with AML [3].

MS can reveal leukemia or occur during the remission or relapse period. It may also precede leukemic manifestations in the peripheral blood or bone marrow.

We present a rare case of an epidural MS revealing chronic myeloid leukemia during the blast phase. We also conducted a literature review on published spinal MS associated with myeloid leukemia in adult patients.

Search strategy

We presented a case report along with the relevant literature regarding spinal myeloid sarcoma in adults. We performed a literature search in PubMed using the terms: “Leukemia, Myeloid” AND “Spine” AND “Sarcoma, Myeloid”. We only included cases with associated leukemia.

We did not include case reports and case series covering MS in children (< 16 years old).

The identified cases are shown in Table 1.

Table 1 Literature review from 1988 to 2020: characterization of spinal myeloid sarcoma associated with leukemia
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Written informed consent for the case to be published was obtained from the patient for publication of this case report.

Case

A 51-year-old man, with no significant medical history, presented with a 2-month history of progressive back pain and bilateral sciatica. He reported a 6-kg weight loss in 2 months.

Physical examination revealed pallor, hepatomegaly, and splenomegaly. His body temperature was 37.1 °C. He had restricted back movement and a positive straight leg raising test. The neurological examination was unremarkable.

The patient underwent magnetic resonance imaging (MRI) of the spine using a 3 Tesla MRI scanner with 3 mm slices.

MRI showed diffuse low signal intensity of spinal bone marrow on T1-weighted images. Epidural masses were also found extending in front of T2, T11, L3, L4, and L5 and were responsible for a slight restriction of the spinal canal with root compression without cord compression (Fig. 1).

Fig. 1
figure 1

Spine MRI showing epidural mass at the L5 level with homogeneous enhancement after the intravenous injection of gadolinium (white arrow) on sagittal fat-suppressed T1-weighted image (a) and iso-intensity (white arrow) on sagittal fat-suppressed T2-weighted image (b). Axial MRI revealing an epidural mass with iso-intensity on T1 (c) and T2 (d) weighted images responsible for bilateral compression of L5 root (arrow head) and a slight restriction of the spinal canal without cord compression

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Laboratory examinations showed anemia (8.7 g/dl), thrombocytopenia (89 × 109/L), and hyperleukocytosis (white blood cell count:83 × 109/L, absolute neutrophil count:60 × 109/L). The serum lactate dehydrogenase and uric acid levels were increased (1897 U/L and 736 μmol/L, respectively). The blast count in the peripheral blood represented 45% of the white blood cells.

The percentage of myeloperoxidase-positive blast cells at the bone marrow cytology was 40%. These blasts were positive for CD13, CD33, CD14, CD4, and CD46.

The cytogenetic study revealed a Philadelphia chromosome.

The blast count in the peripheral blood represented 45% of the white blood cells.

The diagnosis of spinal myeloid sarcoma revealing chronic myeloid leukemia (CML) during the blast phase was established.

The patient underwent induction therapy based on idarubicin (20 mg/day) for 3 consecutive days and cytarabine continuously for 7 days (380 mg/day).

Then, bone marrow cytology revealed less than 3% of blasts which corresponded to a cytological remission. Nilotinib therapy was subsequently initiated.

Three months later, the follow-up MRI showed a complete regression of the epidural masses (Fig. 2). The patient reported a significant improvement in pain.

Fig. 2
figure 2

Spine MRI after 3 months of follow-up showing complete regression of the epidural masses on fat-suppressed T1-weighted image (a) and T2-weighted image (b, c)

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Discussion

Myeloid sarcoma is the result of an extramedullary proliferation of myeloblasts or immature myeloid cells. It can affect 2.4 to 9.1% of patients with acute myeloid leukemia [1, 25]. It may also occur in patients with chronic myelogenous leukemia, especially those with blast crisis and less commonly, in patients with myeloproliferative disorders.

Isolated MS had been reported in patients without underlying hematological disease. These cases may progress to AML within weeks, months, or years. Therefore, these patients require a long-term follow-up.

Myeloid sarcoma may reveal or occur during these diseases, even in patients in clinical remission. Rarely, they can precede the hematological manifestations. The delay between the diagnosis of MS and the onset of leukemia ranged from a few weeks to 16 years [5, 26].

Myeloid sarcomas can affect several sites such as the skin, lymph nodes, paranasal sinuses, orbits, soft tissue, and bone [1, 8]. Spinal involvement is rare, and epidural involvement is even rarer. The cumulative prevalence was about 1% of patients with myeloid leukemia [15]. In a study including 15 patients with spinal epidural masses, only four patients had spinal MS. It was an isolated MS in one case and MS-related to AML in the three other cases [24].

MS is more frequent in children with AML occurring in up to 40% of cases [27, 28]. Interestingly, the male predominance was striking with a male-to-female ratio at 7.8:1 [27]. This difference may be explained by the higher incidence of leukemia in men than in women.

The thoracic and the lumbar spine are the levels frequently affected [29]. Multiple non-contiguous area involvement, as reported in our patient, was also described [27].

Spinal MS can occur as an epidural mass in the central spinal canal, prevertebral mass, along the nerve root course, or as thickening of the nerve root itself. Table 1 summarized cases of spinal MS-related to myeloid leukemia [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]. Among 55 patients with spinal MS, 39 patients had epidural MS. Spinal involvement can cause cord compression or root compression. In our patient, MS was responsible for root compression.

The clinical presentation depends on the level of involvement. It can associate back pain, radicular pain [30], urinary incontinence, numbness weakness, or even acute paraplegia.

Regarding imaging findings, the MRI is the gold standard to assess the epidural involvement. It shows typically epidural mass with iso-intensity on T1-weighted images and isointense or slightly hyperintense signal on T2-weighted images. The enhancement after the injection of gadolinium is usually homogeneous [31, 32].

Diffuse bone marrow infiltration on the MRI suggests the presence of a hematological disorder.

Therefore, the diagnosis of myeloid sarcoma related to leukemia should be considered when MRI shows a diffuse bone marrow signal infiltration associated with multiple epidural masses.

Without evidence of hematological disease, the diagnosis of MS can be challenging. Differential diagnoses include large-cell lymphoma, histiocytic lymphoma, rhabdomyosarcoma, schwannoma, and Ewing sarcoma [5, 33, 34].

Histological findings of MS provide better diagnostic accuracy. However, histological confirmation is not always necessary in patients with Leukemia.

As shown in Table 1, among 55 patients, only 21 patients had histological confirmation of MS.

The pathological study can be carried out on a piece of laminectomy indicated for surgical decompression, an open biopsy, or a computed tomography-guided needle biopsy. However, the biopsy is associated with a risk of dissemination and should be followed by radiation therapy [22].

There are similarities between the cytogenetical findings of MS tissue and the bone marrow, emphasizing that MS derives from the leukemic clone [4].

Moreover, an immunohistochemical panel, including CD34, CD43, CD45, CD117, CD68, lysozyme, and myeloperoxidase, are useful in differentiating MS from other epidural tumors.

Indeed, CD43, lysozyme, myeloperoxidase, and CD68 are the most sensitive markers for MS [35].

Tumor cells can also be detected in the cerebrospinal fluid [11, 21]. However, a lumbar puncture may be dangerous because it can aggravate a neurological deficit and induce paraplegia [27, 36].

In our case, the biopsy was not performed. The MRI findings and the evidence of CML with blast crisis were sufficient to make the diagnosis.

The management of epidural MS is still controversial given the small number of cases. MS should be treated as acute myelogenous leukemia, even if MS is not associated with leukemia [37].

MS is known to be sensitive to both radiation and chemotherapy, but relapses are not rare [38]. The treatment may also include surgical decompression, intrathecal chemotherapy, and allogeneic stem cell transplantation [39].

Surgical treatment, such as laminectomy, is often indicated in patients with neurological deficit. Nevertheless, this treatment can be tricky and may worsen the neurological deficit, notably when MS is located in the cervical spine [20]. The authors suggested that chemotherapy alone is likely insufficient in patients with cord compression [4, 11].

In the absence of cord compression, the treatment may include high doses of steroids followed by radiotherapy and chemotherapy [4]. Indeed, under chemotherapy alone, the epidural mass may progress on the MRI [11], and neurological damage may persist even if hematological remission was obtained [12].

Radiation therapy can be indicated in several situations such as an isolated MS, the inefficiency of chemotherapy, and relapse after hematopoietic cell transplantation [40]. The stereotactic radiosurgery may be indicated for radioresistant spinal tumors, or oligometastatic disease [41]. This treatment requires pathologic confirmation and should be avoided in case of high-grade spinal cord compression. Furthermore, allogeneic stem cell transplantation may improve the survival of patients with MS [42].

In our case, chemotherapy alone leads to MS disappearance on MRI and cytological remission of leukemia.

Despite the regression of the spinal granulocytic sarcoma, the overall survival rate remains low. It depends on the patient’s general status and underlying hematologic disorder [15].

MS is associated with a poor outcome because it represents a sign of CML progression [43].

As shown in Table 1, among 55 patients, 26 patients died (47%). The complete remission of MS was noted in 19 patients.

An early diagnosis may contribute to the improvement of prognosis, mainly neurological damage [23].

In summary, the diagnosis of spinal MS can be very challenging. However, this rare entity should be considered in case of an epidural mass lesion. Bone marrow cytology is required to diagnose the underlying hematological disorder. An early diagnosis is necessary to improve survival rates.