**Question:** A 40-year-old male presents with massive splenomegaly and mild hepatic enlargement. On examination, the peripheral blood film shows cells with hair-like projections. These cells are positive for CD25 and CD103, but negative for CD23. The likely diagnosis is a:

A. Chronic lymphocytic leukaemia
B. Chronic myeloid leukaemia
C. Chronic active EBV infection
D. Chronic lymphocytic choriomeningitis virus infection

**Correct Answer:** C. Chronic active Epstein-Barr virus (EA) infection

**Core Concept:**
Chronic active Epstein-Barr virus (EBV) infection is a viral infection caused by the Epstein-Barr virus (EBV), a member of the herpesvirus family. EBV is known to infect B cells and can lead to various clinical manifestations, including lymphoproliferative disorders, such as lymphomas and leukemias. In this case, the presence of hair-like projections on the peripheral blood film and the immunophenotyping findings (CD25, CD103 negativity) are indicative of the infection by EBV.

**Why the Correct Answer is Right:**
In chronic active EBV infection, the virus infects B cells, causing them to proliferate and form lymphoid aggregates in the spleen and liver. These cells can lead to massive splenomegaly (as seen in this case) and mild hepatic enlargement. The immunophenotyping findings on the peripheral blood film (CD25 positivity and CD103 negativity) are specific to EBV infection. CD25 is a marker for activated T cells, which are involved in the immune response against EBV. On the other hand, CD103 is a marker for dendritic cells, which are not involved in the pathogenesis of EBV infection.

**Why Other Options are Incorrect:**
A. Chronic lymphocytic leukaemia (CLL) and Chronic myeloid leukaemia (CML) are classified under the umbrella of "chronic lymphoproliferative disorders". However, the immunophenotyping findings (CD25 positivity and CD103 negativity) are not indicative of these diseases.

B. While Chronic active EBV infection can cause lymphoproliferative disorders, the immunophenotyping findings (CD25 positivity and CD103 negativity) are not typical for Chronic myeloid leukaemia (CML).

C. Chronic active EBV infection is characterized by the presence of CD25-positive, CD103-negative T cells, which are involved in the immune response against EBV. This option matches the immunophenotyping findings, making it the correct answer.

D. Chronic lymphocytic choriomeningitis (CLCM) is a viral infection caused by LCMV, not EBV. Immunophenotyping findings do not match the characteristics of CLCM.

**Clinical Pearl:**
Chronic active EBV infection is a viral infection that predominantly affects immunocompromised patients, such as HIV patients, organ transplant recipients, or those receiving immunosuppressive therapy. In these situations, the immune