Hypokalaemic Polymyopathy in Burmese cats – Retrospective analysis of cases, new clinical observations and a call for new cases for genomic studies
Fran Musca, Steve Metcalf, Marcus Gunew, Rhett Marshall, Vic Menrath, Richard Malik and Leslie Lyons
Clinical signs referable to hypokalaemia can be seen in a variety of feline diseases, viz. (i) chronic renal disease, (ii) primary hyperaldosteronism and (iii) hypokalaemic polymyopathy. This study focuses on the latter disease, an inherited condition most commonly encountered in young Burmese cats (2-6 months-of-age) which present with signs of myopathic weakness, classically passive ventroflexion of the head and neck, and sometimes also dorsal protrusion of the scapulae, muscle tremor and head bobbing (Jones et al 1988; Lantinga et al 1998). The disease in many respects resembles the human disorder hypokalaemic periodic paralysis, which is characterised by episodic attacks of muscle weakness associated with a transient decrease in blood potassium levels. Reported on for the first time by Eger et al (1983), the condition was shown by Mason et al (1988) to have an autosomal recessive mode of inheritance. The disease has been reviewed by Gruffydd Jones (1997) and more recently by Jones (CVT 14).
In a feline-only practice in Brisbane (Australia), a recent cluster of cases of hypokalaemic polymyopathy in Burmese kittens prompted a review of the clinical manifestations of this condition in comparison of what has been reported in peer reviewed publications and in small animal texts. Additional anecdotal material from the period preceding computerised archiving of case material was provided by Drs Menrath, Metcalf and Malik.
Unlike textbook accounts, it has been our experience that (i) cats can develop genralised weakness without prominent cervical ventroflexion, but with alternative signs e.g. crouching hind limb gait, shifting lameness, stiff/stilted gait; these alternative signs may be present with or without classic signs such as cervical ventroflexion (ii) myalgia can be a prominent (iii) cats can present as adults (iv) the potassium concentration is not invariably low at the time the cat is weak, although serial potassium determinations will eventually detect moderate to severe hypokalaemia (v) marked elevations in creatine kinase activity can provide supportive evidence that hypokalaemia is the underlying problem if the potassium concentration is normal (vi) potassium chloride in large doses (1/2 to 1 Span K [7 mmol KCl] once or twice daily with food) is generally more convenient, less expensive and more effective than potassium gluconate for managing these cases (vii) some cats need on-going therapy, while in others KCl can be discontinued (viii) rarely, cases are refractory to KCl therapy and require low dose prednisolone or acetazolamide to control the clinical signs.
Recognition of this condition relies on a high index of suspicion, although consistent signs in a cat of the Burmese breed is strongly suggestive of this diagnosis. The purpose of this communication is to highlight this condition to small animal clinicians, in an attempt to obtain blood for DNA retrieval from as many cases as possible, with a view to identifying the underlying genetic problem using a whole genome scan and the new feline single nucleotide polymorphism (SNP) microarray, in collaboration with Leslie Lyons and colleagues at UC Davis.
- 1. Eger et al., 1983 C. Eger, W. Robinson and C. Huxtable, Primary aldosteronism (Conn's syndrome) in a cat; a case report and review of comparative aspects, ... – if you read this, at the end they talk about the Burmese cats
- 2. Mason K V (1988) Hereditary potassium depletion in Burmese cats. Journal of the American Animal Hospital Association 24, 481
- 3. Gruffydd-Jones et al (1997) Proceedings of the 14th American College of Veterinary Internal Medicine (ACVIM), San Antonio, Texas p 757
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- 7. Lantinga E, Kooistra HS, van Nes JJ. 1998 Periodic muscle weakness and cervical ventroflexion caused by hypokalemia in a Burmese cat. Tijdschr Diergeneeskd. 123(14-15):435-7.
Figure 1 Affected cat being supported against gravity. Note prominent ventroflexion of the head and neck.