Incidence of and risk factors for seizures after myelography performed with iohexol in dogs: 503 cases (2002–2004)

Ronaldo C. da Costa, Joane M. Parent and Howard Dobson

Background
Myelography is a diagnostic imaging technique for spinal cord disorders in dogs, but it can cause complications, including seizures. Iohexol, a second-generation nonionic contrast agent, is commonly used for its safety profile, though some studies report a seizure incidence of up to 21.4%. This study aimed to determine the incidence and risk factors for seizures following myelography using iohexol in dogs.

Methods
A retrospective case series analyzed medical records from 503 dogs that underwent myelography at the Ontario Veterinary College between 2002 and 2004. Data collected included breed, weight, iohexol dose and volume, injection site, lesion location, anesthesia details, and seizure occurrence. Statistical analyses examined potential risk factors.

Results
Postmyelographic seizures occurred in 15 of 503 dogs (3%). Key risk factors included:

Dog size: Large dogs had a significantly higher seizure risk, 35.35 times that of small dogs.
Injection site: Cerebellomedullary cistern injections were 7.46 times more likely to cause seizures than lumbar injections.
Lesion location: Dogs with cervical spinal lesions had 4.65 times the risk compared to other regions.
Iohexol volume: A higher total volume increased seizure likelihood; doses >8 mL were associated with most seizures. Doberman Pinschers and Rottweilers exhibited higher seizure rates.

Limitations
The study's retrospective design relied on medical record completeness, and the sample size for some subgroups (e.g., dogs with multiple injections) limited the power to detect multivariate interactions.

Conclusions
Large dogs, cervical lesions, and cerebellomedullary cistern injections are significant risk factors for postmyelographic seizures. Limiting iohexol volume to ≤8 mL and favoring lumbar injections could reduce risk. Despite the identified risks, myelography remains relatively safe with proper precautions.

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