Dr Margie Scherk
DVM DipABVP (Feline Practice)
Straining in the litter box, possibly even crying out…or leaving unwelcome hard pellets around the home. Who wants any of it? Constipation is unpleasant at all levels. It is uncomfortable, can interfere with appetite and, in cats, can even result in vomiting. Traditional approaches to this hard problem include administration of enemas, laxatives to soften the stool or increase contractions, dietary fiber, and promotility agents. Might we be missing something really basic? And when should we be concerned about long-term effects of constipation?
Aetiologies for constipation
Constipation is a clinical sign that is not pathognomonic for any particular cause. Constipation increases with increasing age, so that older cats in a UK shelter study were found to be at greater risk. This study also showed a role of season: more constipation was seen during the winter. Most commonly, constipation is a result (and sign) of dehydration. The body is 65-75% water, depending on age and % body fat. Homeostasis attempts to maintain a consistent cellular and extracellular environment; when cells become dehydrated, the body takes steps to correct the fluid deficit. Drinking more and concentrating urine are helpful, but once those capabilities have been maximised, water is reabsorbed in the colon resulting in drier stool that is harder to pass. Bearing this in mind, medical therapy might not be the best initial therapeutic approach.
As well, other causes for constipation include problems that result in obstruction, (either mechanical or functional), painful defecation, stress within with the home environment (social or a dirty toilet) and possibly metabolic disease. (See Table 1)
Evaluating the patient: history, physical examination and diagnostic testing
Given the myriad of possible causes as well as concurrent problems, getting an appropriate history is very important. Clients may misinterpret stranguria for tenesmus. Not only is current diet (type, frequency, appetite) important, but also questions to determine whether the patient might be dehydrated (due to decreased intake or increased water loss), may have orthopaedic pain or may be disinclined to use the litter box due to social or toileting factors (fear, unpleasant box). Table 2 addresses these possible concerns at length.