Background

Sciatica is an archaic term with a nebulous meaning.1 For most clinicians, it refers to a radiculopathy affecting the sciatic nerve but confusingly is used more generally to describe pain that radiates from the lower back down the leg. It is a common condition with a lifetime incidence of 13–40% and in up to 90% of cases, it occurs due to intervertebral disc herniation.2 ,3 On rare occasion, mass lesions involving the sciatic nerve or lumbosacral plexus can also produce sciatica-like symptoms. Diagnosis of sciatica and its aetiology in the clinic can be challenging. The straight leg raise (SLR) test is often thought to be pathognomonic for sciatica caused by lumbar disc herniation; however, it has poor sensitivity and specificity compared with MRI of the lumbar spine, which is the gold standard investigation.4

Granulocytic sarcoma, also known as myeloid sarcoma or chloroma, is a rare solid tumour consisting of haematological cells from the myeloid lineage. It is known to be an extramedullary manifestation of acute myeloid leukaemia and can present de novo or as a relapse of acute myeloid leukaemia following stem cell transplantation.5 ,6 Less commonly, it is seen in patients with myelodysplastic syndrome and chronic myeloid leukaemia.7 ,8 The locations affected are diverse, with the most common being bone, periosteum, soft tissue, lymph node and skin.9 More rarely, the genitourinary system and nervous system can be involved.10–21

Case presentation

A man aged 56 years presented to the emergency department with a 4-month history of right buttock pain radiating down the right leg treated as sciatica in the community. Two weeks prior to admission, the pain had worsened to the extent that he needed a walking stick to mobilise. He had also developed nocturnal pain and allodynia throughout the outer aspect of the right leg and noticed a tender lump in his right buttock. This had not been present on previous visits to his general practitioner, but on discovery, he was promptly referred to the emergency department for further assessment.

He developed myelodysplastic syndrome (RAEB-2) aged 49 and underwent chemotherapy (daunorubicin+cytarabine) and allogeneic bone marrow transplant. This subsequently failed and he required more chemotherapy (FLAG-Ida+cytarabine) and a second allogeneic bone marrow transplant. He had been in remission until the time of presentation.

On examination, a hard, smooth tender mass was palpable in the upper half of the right buttock. The posterolateral aspect of his right buttock and thigh were very painful to touch. He had weak right knee flexion with total loss of movement in the ankle and on knee extension. The right ankle reflex was absent. The left lower limb was neurologically normal. The SLR test was negative bilaterally. Admission blood test results are shown in table 1.

An MRI of the lumbar spine performed 6 weeks prior to admission had shown mild lumbar disc protrusions at L3/4 and L5/S1 with a disc prolapse at L4/5. There was no evidence of significant neurological compromise or bone marrow abnormality. On admission, after detecting the buttock mass on clinical examination, an informal ultrasound scan was performed in the emergency department and showed a 4×10 cm heterogeneous hypoechoic mass in the right buttock (figure 1). Subsequent MRI of the right buttock revealed a heterogenous enhancing soft tissue mass lesion along the right lateral wall of the pelvis extending through the sciatic and obturator foramina into the thigh and engulfing the lumbosacral plexus measuring 18×12×10 cm (figure 2A, B). A second mass lesion involving the gluteal muscles was also identified and seen to communicate with the pelvic mass. Unfortunately, the first MRI examination of the lumbar spine did not extend caudally enough to capture the mass, leading to a delay in diagnosis.

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Figure 1

Ultrasound scan demonstrating heterogeneous hypoechoic mass in the right buttock.

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Figure 2

(A) Axial T2-weighted MRI demonstrating an ill-defined mass lesion* along the right lateral wall of the pelvis adjacent to the seminal vesicles, lower rectum and anal canal extending through the sciatic foramen into the thigh and through the obturator foramen. (B) Coronal T1-weighted MRI demonstrating a right gluteal mass* communicating with a right pelvic mass.

A biopsy performed at a tertiary orthopaedic centre demonstrated a granulocytic sarcoma. He was subsequently referred to haematology for further investigations and treatment.

•  RAEB-2: refractory anaemia with excess blasts 2

•  FLAG-Ida: a combination of fludarabine, cytarabine+idamycin