This category includes following disorders:

• Systemic EBV-positive T-cell lymphoma of childhood
• Hydroa vacciniforme lymphoproliferative disorder
• Severe mosquito bite allergy
• Systemic chronic active EBV disease

Systemic EBV Positive T cell Lymphoma of Childhood

• It is a rapidly progressive life threatening disease
• Common in Asia, especially in Japan
• Caused by EBV
• Presents with hepatosplenomegaly, weeks to months following infectious mononucleosis.
• Rapidly progresses to hemophagocytic syndrome, coagulopathy, multiorgan failure and sepsis.
• Tumor cells are small and lack significant cytologic atypia
• Positive for CD2, CD3, TIA1, CD8
• Poor prognosis
• Treatment: HLH type protocol followed by allogeneic stem cell transplantation

Hydroa Vacciniforme lymphoproliferative disorder

• It is a EBV positive cutaneous T cell lymphoma occurring in children
• Common in Asians and native Americans
• Presents with papulo-vesicular eruptions, precipitated by sunlight or insect bite.
• Systemic symptoms include fever, wasting, lymphadenopathy and hepatosplenomegaly.
• Morphology
  • Small to medium sized cells with no significant atypia
  • Infiltration extending from epidermis to subcutis showing necrosis, angiocentricity and angioinvasion.
• IHC- Positive for T cell markers and CD56
• EBER- in situ hybridization- Positive
• Treatment:
  • Early-stage: conservative treatment with photoprotection and topical steroids
  • Systemic disease:
    • Immunomodulators: thalidomide, antivirals, interferon
    • Haematopoietic stem cell transplantation

Severe mosquito bite allergy

• It is an EBV-positive NK-cell (or occasionally T-cell) lymphoproliferative disorder characterized by high fever and severe skin manifestations including bullae, ulcers, necrosis, and scarring after mosquito bites.
• Extremely rare
• Increased risk of developing haemophagocytic lymphohistiocytosis, systemic chronic active EBV disease, aggressive NK-cell leukaemia, and extranodal NK/T-cell lymphoma.

Systemic chronic active EBV disease

• It is systemic proliferation of polyclonal, oligoclonal, or (often) monoclonal EBV-positive T or NK cells with persistence of symptoms of more than 3 months in duration.
• Various clinical manifestations:
  • Indolent
  • Localised forms: Hydroa vacciniforme lymphoproliferative disorder and severe mosquito bite allergy to more 
  • Systemic disease: fever, hepatosplenomegaly, and lymphadenopathy, HLH
• Poor prognosis
• Treatment: Haematopoietic stem cell transplantation