Pseudolymphoma in a cat on phenobarbital treatment

A two-year-old female spayed domestic shorthair cat was presented with apathy, inappetence and generalised lymphadenomegaly. Anamnestic data included a generalised seizure disorder and phenobarbital treatment started one month before presentation. Routine blood analysis revealed only mild abnormalities and FeLV and FIV tests were negative. Both popliteal lymph nodes were aspirated and cytology was consistent with reactive lymph node hyperplasia. PCR for antigen receptor rearrangement testing diagnosed a polyclonal cell population. In the absence of another cause, lymphadenomegaly was attributed to an adverse drug reaction and phenobarbital was discontinued. The cat's condition improved and lymph node size normalised over the next 10 days. The retrospective diagnosis was phenobarbital-induced pseudolymphoma.