Suspected Phenobarbital-Induced Pseudolymphoma in a Dog

Area of Science:

• Veterinary Medicine
• Pharmacology
• Oncology

Background:

• Pseudolymphoma is a known adverse drug reaction to anti-epileptic medications in humans.
• While reported in cats, this condition has not been previously documented in dogs.
• Phenobarbital is a common anti-epileptic drug used in canine medicine.

Observation:

• A 2.5-year-old Shepherd mix presented with ataxia, lethargy, and fever, later developing generalized lymphadenopathy.
• The dog was being treated with phenobarbital and levetiracetam for epilepsy, with serum levels within therapeutic ranges.
• Diagnostic imaging revealed hepatomegaly, splenomegaly, and lymphadenopathy; cytology indicated reactive lymph nodes and inflammation.

Findings:

• Discontinuation of phenobarbital resulted in rapid resolution of fever within 24 hours and complete clinical improvement within a week.
• The clinical presentation mimicked neoplasia, highlighting the importance of considering drug reactions.
• This case suggests phenobarbital can induce pseudolymphoma in dogs, an idiosyncratic adverse reaction.

Implications:

• This case highlights a potentially serious, yet reversible, adverse reaction to phenobarbital in dogs.
• Veterinarians should consider phenobarbital-induced pseudolymphoma as a differential diagnosis in dogs presenting with lymphoma-like signs.
• Early recognition and drug withdrawal can prevent misdiagnosis and ensure prompt recovery.