Seizures in four-week-old puppies are uncommon, but they can arise from many sources, including fever, hypoglycemia, parasites, reactions to food or foreign substances, heredity, and idiopathic epilepsy. Because of the puppy's relative fragility, a veterinarian should examine the puppy, regardless of what the owner might feel caused the seizure to occur in the first place.
The normal canine temperature hovers between 99.5 and 102.5 degrees Fahrenheit. Any body temperature above 103 degrees is considered a fever. Small puppies are inefficient at temperature regulation. Even small changes, such as teething, can cause low-grade fevers. High fevers, however, can trigger seizures in puppies. A high fever can indicate a serious underlying cause, such as infection, distemper or parvovirus, so a puppy with a high fever must be taken to the veterinarian for proper diagnosis of the cause.
Puppies, especially small breed puppies, are susceptible to incidents of hypoglycemia (low blood sugar). According to the Epi Guardian Angels, "hypoglycemia can be a life-threatening--even fatal--condition, and is known to be a cause of canine seizures. The occurrence of symptoms depends on how far, and how fast, the blood sugar has dropped." They go on to explain that hypoglycemia is a significant potential risk in small breed puppies (See References 2, Hypoglycemia--Low Blood Sugar).
Puppies are prone to parasites of many kinds, particularly those transmitted by the mother. Some parasites cause damage to organs, potentially causing seizures, while others have an effect on puppies being able to properly utilize the nutrients they require to stay healthy.
Four-week-old puppies are unused to processing their own food, therefore, their bodies might see food itself as a foreign substance. In addition, puppies might show sensitivities to certain ingredients or additives in commercial food. An elimination diet, created under a veterinarian's or canine dietician's guidance, can help identify food allergy problems.
Most four-week-old puppies are unlikely to go outside unattended, potentially ruling out toxins such as mushrooms, snakebites, and other outside hazards. Many dangerous substances exist inside the house, however, such as ant, roach, or rodent traps, cigarette butts, and various foods. Chocolate, raisins, onions, and coffee are foods and beverages that humans regularly consume that could have toxic effects on developing puppies. Flea and tick remedies should not be used on small puppies.
Idiopathic epilepsy is has no known cause. Some epilepsy of unknown causes might be genetic, passed down through generations undetected. Idiopathic epilepsy may be transient, causing one seizure and never again affecting the puppy through its lifetime.
At times, dogs will experience seizures due to trauma, such as head injuries from falls. They may also have underlying physical causes, such as brain tumors or deformities. In these cases, surgery is often required. Dogs with seizures due to these causes may have an improved prognosis, or even see an end to seizures, once the physical issue that is causing the seizures is dealt with or removed.