Usually appearing after the age of 60, the first symptom of AD is impaired memory formation, especially for recent events or newly learned information. Memory lapses may be very subtle at first, thus leading many people to discount the symptoms as a sign of getting old. A person may ask the same question or say the same thing repeatedly within a short period of time but without remembering the prior conversation. Important objects such as checkbooks or wallets may be misplaced and lost. In the kitchen, pots can be left on the stove resulting in burnt food or small fires.
As AD progresses, details or even the occurrence of recent events may be forgotten. Implicit (or memory for overlearned activities like riding a bike) and semantic memory (fact memory), as well as long-term memory, remain relatively intact early, but decline in these forms of memory eventually develops.
While memory is a key feature, AD is also defined by a decline in visuospatial skills, language, abstraction, planning and organization. Visuospatial problems may cause a person to become disoriented or lost in familiar environments. Accidents or becoming lost while driving can occur. Inability to recognize familiar individuals may also develop. Language problems such as word-finding difficulty occurs early but impaired comprehension or decreased speech output may occur in the later stages. Declines in planning and organization often result in missed bill payments and difficulty handling finances.
Behavioral symptoms are also common in AD. Apathy or decreased motivation causes affected individuals to appear lazy and indifferent. Depression is also common. In some cases, the onset of depression late in life may precede the cognitive symptoms of AD. Agitation including physical and verbal aggressiveness may develop, usually later in the illness. Delusions and hallucinations can appear at any stage of Alzheimer's, but usually occur a few years after AD is diagnosed. In rare instances, patients may believe that familiar people have been replaced with imposters.