Polioencephalomalacia
Polioencephalomalacia is damage to the grey matter of the brain, most often from vitamin B1 (thiamine) problems or excess sulfur, seen mainly in sheep, goats, cattle and camelids.
The word looks impenetrable, but it breaks down neatly: "polio" means grey, "encephalo" means brain, and "malacia" means softening. Polioencephalomalacia, often shortened to PEM and also called cerebrocortical necrosis, describes damage and death of cells in the grey matter of the brain, the outer layer that handles vision, awareness and coordinated movement. It is a description of what has happened to the brain rather than a single disease with a single cause.
PEM turns up most often in ruminants, the animals that ferment their food in a rumen. The Merck Veterinary Manual describes it as a common neurological disease of ruminants worldwide, affecting cattle, sheep, goats, deer and camelids such as alpacas, and links it chiefly to thiamine (vitamin B1) deficiency or sulfur toxicity. Thiamine matters because the brain needs it to turn sugar into energy, and without that energy brain cells swell and die. Healthy ruminants normally make their own thiamine with the help of rumen microbes and store very little of it, so anything that upsets the rumen can tip an animal into deficiency within days. Common triggers include an abrupt switch to grain-heavy feed, plants containing the thiamine-destroying enzyme thiaminase such as bracken fern and horsetail, high sulfur levels in feed or water, lead poisoning, salt poisoning or water deprivation, and overdosing of the coccidiosis drug amprolium.
In dogs and especially cats, a related problem exists under a different name: thiamine deficiency encephalopathy, which damages specific deep brain areas rather than the cortex. Cats are vulnerable because they need relatively more thiamine than most species, and cases have been traced to all-meat or raw-fish diets, home-cooked food, and commercial food that was poorly processed or stored, since thiamine breaks down easily with heat and time.
Signs that need a vet the same day
Whatever the species, PEM looks like a brain in trouble, and the signs come on fast:
- A wobbly, drunken gait, stumbling, or falling over
- Apparent blindness while the pupils still react to light
- Head pressing against walls, or a "stargazing" posture with the head tilted back
- Squinting or abnormally positioned eyes, tremors, circling
- In cats and dogs, early appetite loss and vomiting before the neurological signs appear
- Collapse, seizures and coma in advanced cases
Treatment is injectable thiamine, alongside correcting whatever caused the problem, and time is everything. Animals treated early often improve strikingly within a day or two, while those treated late can be left with permanent damage or die. That is why any sudden blindness, staggering or seizure deserves an emergency call rather than a wait-and-see approach. A vet can also rule out the many other conditions that look similar, including listeriosis, lead poisoning and infectious brain disease. This entry is general information, and diagnosis needs hands-on examination.