What is a neutrophil inclusion body?

Neutrophil Inclusion Bodies: Definition and Clinical Significance

Neutrophil inclusion bodies are abnormal intracytoplasmic structures found within neutrophils that can indicate various pathological conditions, ranging from dysplastic processes to critical illness with impending mortality.

Types of Neutrophil Inclusion Bodies

Howell-Jolly Body-Like Inclusions

• These appear as detached nuclear fragments within the cytoplasm of mature neutrophils, resembling the Howell-Jolly bodies typically seen in red blood cells 1
• They are thought to represent dysplastic granulopoiesis and have been associated with:
  • Myelodysplastic syndrome (MDS), where they appear in <5% of mature neutrophils in 72% of MDS cases 1
  • HIV infection and immunosuppression 2, 1
  • Post-transplant immunosuppression, particularly in patients receiving tacrolimus and steroids for graft-versus-host disease (GVHD) 2
  • Antiviral medications, especially nucleoside analogs 1

Critical Green Inclusions

• These are bright green or blue-green cytoplasmic inclusions with variable sizes, blocky appearance, and ill-defined borders 3, 4
• They represent lipid-rich material, likely derived from lipofuscin-like substances released from necrotic liver parenchymal cells 4
• Critical prognostic significance: 65% of patients with green inclusions died within days of detection 4
• Almost universally associated with:
  • Acute liver failure (ischemic or hypoxic hepatitis) 3, 4
  • Lactic acidosis 3, 4
  • Impending patient death 3, 4

Clinical Context and Recognition

When to Suspect Inclusion Bodies

• In immunocompromised patients, particularly those post-transplant or on immunosuppressive therapy 2
• In patients with acute liver failure and metabolic derangements 3, 4
• In patients with myelodysplastic syndrome during bone marrow evaluation 1

Diagnostic Approach

• Peripheral blood smear examination is the primary method for identifying these inclusions 2, 3, 4
• Green inclusions are easy to identify due to their distinctive color and should be actively reported by laboratories 4
• Howell-Jolly body-like inclusions require careful examination as they appear in only a minority (<5%) of neutrophils 1

Critical Clinical Implications

The presence of green neutrophil inclusions should trigger immediate clinical correlation, as they indicate a critically ill patient with high mortality risk 3, 4. These findings should prompt:

• Assessment for acute liver failure and hepatic ischemia 4
• Evaluation of lactate levels and metabolic status 3, 4
• Recognition that the patient may be in a pre-terminal state requiring intensive supportive care 4

Common Pitfall

Do not dismiss small cytoplasmic inclusions in neutrophils as artifacts—they may represent either dysplastic changes (Howell-Jolly body-like) or critical illness markers (green inclusions), both requiring clinical attention and correlation 3, 4, 1.