Can leukemic cells infiltrate into the soft tissue of the leg in a patient with leukemia?

Can Leukemic Cells Infiltrate Soft Tissue of the Leg?

Yes, leukemic cells can definitively infiltrate into the soft tissue of the leg, though this represents an uncommon extramedullary manifestation of leukemia that requires systemic chemotherapy rather than local treatment alone.

Extramedullary Leukemic Infiltration: Overview

Leukemic cells can infiltrate virtually any extramedullary site, including soft tissues of the extremities, though this occurs less frequently than involvement of lymph nodes, skin, and bones 1, 2. When this occurs, it represents a serious manifestation requiring aggressive systemic therapy 3.

Myeloid Sarcoma (Granulocytic Sarcoma)

Myeloid sarcoma is the most well-characterized form of soft tissue leukemic infiltration, occurring in 5-7% of patients with acute myeloid leukemia (AML). 2

• These are tumor masses consisting of myeloid blasts that efface tissue architecture at anatomical sites other than bone marrow 1
• Most commonly involve skin, lymph nodes, gastrointestinal tract, bone, and soft tissue 1
• Require systemic AML-directed chemotherapy, not just local treatment, as emphasized by the American Society of Hematology 3
• Distinguished from frank AML by having less than 20% bone marrow blasts 3

Intramuscular Leukemic Relapse (ILR)

Intramuscular involvement, while very unusual, is a documented phenomenon with specific clinical and radiologic features. 4

Clinical Presentation

• Manifests as focal pain, swelling, and muscle weakness in the affected area 4
• Most commonly involves the extremities (44% of cases) 4
• Acute myeloid leukemia is the most common underlying diagnosis 4

Radiologic Features

• Diffuse muscle infiltration is the most common imaging pattern 4
• On MRI: hypointense to isointense on T1-weighted images, hyperintense on T2-weighted images 4
• Demonstrates homogeneous enhancement on post-contrast CT/MRI 4
• CT and MRI are both effective for detection and characterization 4

Other Leukemia Types and Soft Tissue Involvement

Plasma cell leukemia (PCL) can also involve soft tissues, though this is exceedingly rare. 5

• Extramedullary involvement including soft tissue is documented but extremely uncommon 5
• One case report describes subcutaneous nodules in pelvic and gluteal regions with PCL 5
• PCL has high frequency of extramedullary involvement overall, making imaging evaluation with MRI or PET/CT important 1

Hairy cell leukemia typically infiltrates bone marrow and spleen but may extend to other sites. 1

• Leukemic cells may be found in liver and lymph nodes 1
• Peripheral lymphadenopathy is uncommon 1

Diagnostic Approach

When to Suspect Soft Tissue Leukemic Infiltration

Consider this diagnosis in any patient with known leukemia who develops:

• New focal pain, swelling, or mass in an extremity 4
• Muscle weakness localized to a specific region 4
• Palpable soft tissue masses 6

Diagnostic Workup

Tissue biopsy is essential for definitive diagnosis, as leukemic infiltration can mimic other conditions. 6

1. Imaging studies:

   • MRI is preferred for soft tissue characterization 4
   • CT can identify masses and assess enhancement patterns 4
   • Look for diffuse muscle infiltration or discrete masses 4

2. Biopsy with proper specimen handling:

   • Fresh specimens should be obtained when possible 6
   • Touch imprints should be performed 6
   • Immunohistochemistry is crucial for lineage determination 1, 3
   • Flow cytometry helps characterize blast phenotype 3

3. Systemic evaluation:

   • Bone marrow examination to assess marrow involvement 3
   • Complete blood count with differential 7
   • Imaging to identify other extramedullary sites 1

Critical Pitfalls to Avoid

Extramedullary leukemia presenting as soft tissue masses can be misdiagnosed as lymphoma or other solid tumors, especially when clinical history is not available. 3, 6

• Systematic specimen handling and proper triaging are keys to reducing diagnostic error 6
• Immunochemical methods are essential to demonstrate leukemic cells in tissue 8
• Do not treat with local therapy alone—systemic chemotherapy is required 3

Treatment Implications

Any soft tissue leukemic infiltration requires systemic chemotherapy directed at the underlying leukemia. 3

• Local treatment alone is inadequate 3
• Decreasing joint or soft tissue pain is often the first sign of clinical response to chemotherapy 8
• The presence of extramedullary disease may indicate more aggressive disease requiring intensified therapy 1