Suspected Phenobarbital‐Induced Pseudolymphoma in a Dog

Abstract

Pseudolymphoma is a drug reaction to anti‐epileptics that is well recognized in humans; it has been reported in one cat but not dogs. In this report, lymphoma‐like clinical signs are suspected to be secondary to phenobarbital administration in a dog. A 2.5‐year‐old male, neutered Shepherd mix presented for a 3‐day history of progressive ataxia, dazed mentation, pyrexia, and lethargy. While hospitalized, the dog developed generalized lymphadenopathy and sustained pyrexia. The dog was receiving levetiracetam and phenobarbital for epilepsy, and serum concentrations of both were within standard therapeutic ranges. Abdominal ultrasound revealed hepatomegaly, splenomegaly, and generalized lymphadenopathy. Cytology of the peripheral lymph nodes was consistent with reactive lymph nodes, and aspirates of the liver and spleen revealed histiocytic‐neutrophilic inflammation. Phenobarbital was discontinued and replaced with zonisamide. Within 24 hours, the dog was normothermic, and other clinical signs resolved within a week. This case highlights a potentially serious yet reversible adverse reaction to phenobarbital in a dog. This idiosyncratic reaction could be mistaken for neoplasia and is an important differential for lymphoma‐like signs in any dog administered phenobarbital.

Suspected phenobarbital‐induced anticonvulsant hypersensitivity syndrome in a cat

“…1 However, in veterinary medicine, there are only a few case reports. Thus far, there are four documented cat cases [2][3][4][5] and one dog case 6 reporting lymphadenopathy post administration of phenobarbital. Clinically, one of the important differential diagnoses of lymphadenopathy is lymphoma.…”

Phenobarbital-induced anticonvulsant hypersensitivity syndrome in a cat

“…Anticonvulsant hypersensitivity syndrome (AHS) is a delayed adverse drug reaction associated with the use of aromatic anticonvulsant drugs [4,5,7]. It is mainly caused by drugs such as phenytoin, phenobarbital, and carbamazepine.…”

“…Phenobarbital was replaced with levetiracetam, and no lymph node enlargement was observed after 10 days [8]. Although mild symptoms of AHS can be self-limiting, AHS in dogs or cats should be monitored carefully [1,7].…”

Suspected phenobarbital-induced fever in a cat

“…[5][6][7][8][9] Pseudolymphoma secondary to phenobarbital administration has been reported in one dog and two cats, characterized by fever and generalized lymphadenopathy that resolved after discontinuation of the medication. [10][11][12] A recent report of similar signs in a cat occurred during treatment with multiple anticonvulsants and resolved after discontinuation of zonisamide. 13 Both onset and resolution of clinical signs in dogs, cats and humans typically occur within several weeks of starting and subsequently discontinuing the medication.…”