Hemophagocytic lymphohistiocytosis

Haemophagocytic lymphohistiocytosis (HLH), also known as macrophage activation syndrome, is a nonmalignantnon-malignant disorder of immune regulation characterised by overproduction of cytokines and diminished immune surveillance. It may affect multiple organs and is one of the few entities which demonstrate histiocytic emperipolesis on light microscopy.

Epidemiology

It typically affects infants and children, as well as adult patients post-transplant ⁵.

Pathology

The condition can be primary or secondary. The primary form is thought to have an autosomal recessive inheritance pattern, but with many instances of sporadic occurrence.

The secondary form may occur with several conditions such as ⁵:

• malignancy
• post-transplantation, particularly with PTLD
• infection: viral, bacterial, fungal, or parasitic
• drug exposure
• systemic lupus erythematosus
• Still disease
• Griscelli-Prunieras syndrome
• Chediak-Higashi syndrome

Associations

• EBV infection ^2.3
• solid organ transplantation ^10,11
• pulmonary hypertension ⁸

Clinical presentation

Systemic symptoms can be non-specific but patients can have pancytopenia, coagulopathy, and organomegaly,

Radiographic features

Chest

Chest radiographs may show alveolar-interstitial opacities with pleural effusions, often with rapid evolution and resolution.

Abdomen

Hepatosplenomegaly, gallbladder wall thickening, hyperechoic kidneys and ascites are are common abdominal findings.

Brain

Non-specific periventricular white-matter abnormalities, brain-volume loss and enlargement of extra-axial fluid spaces may be seen. Orbital myopathy has also been described.

History and etymology

It is thought to have been first reported by in 1952 by Farquhar and Claireaux who at that time called the disease familial hemophagocytic reticulosis ¹¹.