Thiamine deficiency
2 March 2017
Following the recent recall of four dried cat food products due to low thiamine levels, BSAVA wanted to provide a brief update on thiamine deficiency.
Thiamine deficiency
Thiamine (vitamin B1) deficiency occurs most commonly in anorexic cats or cats that are fed an all fish diet containing thiaminase. However, it but has also been associated with excessive cereal in the diet, uncooked soy products, heating foods to excessive temperatures and the use of sulphur dioxide as a preservative. Thiamine deficiency can also occur in dogs.
Thiamine plays an essential role as a cofactor for enzymes in carbohydrate metabolism, it forms a compound with ATP to form thiamine diphosphate/thiamine pyrophosphate. It does not affect blood glucose. Thiamine deficiency leads to energy depletion and neuronal necrosis resulting in polioencephalomalacia, particularly of the oculomotor and vestibular nuclei, the caudal colliculus and the lateral geniculate body.
Clinical signs
Early, non-specific signs typically include lethargy and inappetence. The earliest neurological sign is bilateral vestibular ataxia, which manifests as an abnormal broad based stance, a ventroflexed neck in cats and loss of balance. There may be evidence of central vestibular syndrome (nystagmus and strabismus) as well as tremors or seizures. There may also be ocular signs including bilateral pupillary dilation, peripapillary oedema and papillary neovascularisation.
If untreated, signs progress to semi-coma, persistent vocalization, opisthotonus and death.
(Image above shows ventroflexion of the head and neck of a cat presented with central vestibular disease due to thiamine deficiency. Courtesy S Platt).
Diagnosis
Diagnosis is usually based on clinical history, suggesting a thiamine deficient diet and clinical signs.
It is possible to measure blood thiamine levels, although these may not reflect tissue levels. As this test is not widely commercially available and sample and storage requirements may vary it is important to check with the diagnostic laboratory before submitting samples.
Bilaterally symmetrical haemorrhage and malacia of susceptible areas of the brain may be detected by MRI or at post-mortem.
Treatment
Thiamine deficiency can be treated with thiamine supplementation. Where diet is considered to be a factor a more appropriate diet should be introduced. In the early stages of disease, treatment can lead to the rapid reversal of clinical signs, although some signs, such as blindness and wide excursions of the head and neck can be residual.
Thiamine (Vitamin B1) is available as a 100 mg/ml solution (authorized for veterinary use, though only in farm animals), as well as various oral preparations.
Dosage
Cats: Vitamin B1 deficiency: 10-25 mg/cat i.m., s.c. q12-24h for several days until signs resolve or 10-20 mg/kg i.m. until signs resolve then 10 mg/kg p.o. for 21 days.
Dogs: Vitamin B1 deficiency: 50-250 mg/dog i.m., s.c., p.o. q12-24h for several days until signs resolve.
Contra-indications and warnings
- Anaphylaxis can be seen with intravenous use; dilute with fluids and/or give slowly if using i.v.
- Adverse effects in pregnant animals are documented – Do not use in pregnant animals unless absolutely necessary.
- There are no specific clinical interactions reported, although thiamine may enhance the activity of neuromuscular blocking agents.
Further information
BSAVA Manual of Canine and Feline Neurology, 4th edition
BSAVA Small Animal Formulary, 8th edition – book or online (BSAVA members only)