If you have a relative who has Alzheimer's disease, you may have heard about how many conditions can be misdiagnosed as Alzheimer's, when in fact those conditions are a lot more treatable. However, another problem is that those conditions can also be missed if the person develops them after being correctly diagnosed with Alzheimer's. While doctors do try to ensure they know about everything going on health-wise with an Alzheimer's patient, sometimes the doctors aren't always able to keep an eye on the behavior of every patient every minute of the day -- and at least one of these symptoms can come on very quickly. Here are three conditions and symptoms that you should look out for when you see your relative.

B12 Deficiency

A severe deficiency of vitamin B12 can lead to dementia-like symptoms, and in fact, there have been cases of the deficiency being misdiagnosed as dementia. However, because the symptoms, such as confusion, mimic those of dementia's so strongly, it's easy to miss a forming deficiency in someone who already has Alzheimer's. And this is possible even if the person is eating a balanced diet with good B12 sources; people can develop pernicious anemia, or an inability to absorb as much B12, as they get older.

Look for a sudden worsening of dementia symptoms, especially the onset of major symptoms that the person didn't have before, such as numbness in the hands and feet. B12 deficiency can be determined by a simple blood test, so if you do see a sudden worsening, it's best to ask the patient's doctors for a test.

Normal Pressure Hydrocephalus

This very common condition involves fluid buildup in the brain and is often misdiagnosed as Alzheimer's. But developing actual Alzheimer's doesn't prevent NPH from developing later on. If the patient suddenly develops an odd gait, like he or she is trying to balance much more carefully while walking, talk to the doctors about the possibility of NPH.

Diabetes

Undiagnosed diabetes can be frightening because it sometimes leads to the person suddenly acting very drunk and confused if their blood sugar is low. There have been cases of people being pulled over for drunk driving only for the police to determine it was severe diabetes-related hypoglycemia. If all of a sudden your relative appears drunk, get emergency help immediately in case it is undiagnosed diabetes.

If you have other questions about Alzheimer's care or the possibility of developing these other conditions and the possibility that these conditions could be missed, talk to the relative's doctor. He or she can try to do extra monitoring if you're really concerned or let you know about other symptoms to be on the lookout for.