Early-onset Alzheimer's disease: Although the patient's CT scan, MOCA, and MMSE are normal, early-onset Alzheimer's can present with subtle cognitive decline, particularly in memory and language, before significant changes are evident on standard cognitive tests or imaging. The normal imaging and cognitive screening tests do not rule out early Alzheimer's, as they can be insensitive to early disease.

Depression or Anxiety: These conditions can significantly impair cognitive function, including memory and word finding, and are common in middle-aged adults. Normal cognitive screening tests do not exclude these diagnoses, as they can affect performance in subtle ways not captured by these tests.
Sleep Disorders: Sleep apnea, insomnia, or other sleep disorders can lead to cognitive impairments similar to those described, including difficulty with memory and word finding.
Hypothyroidism: This condition can cause cognitive symptoms, including memory problems and difficulty with concentration, which might be mistaken for primary cognitive disorders.

Brain Tumor or Cerebral Vasculitis: Although the CT scan is normal, it's crucial to consider the possibility of a brain tumor or cerebral vasculitis, as these conditions can present with focal cognitive deficits and may not always be visible on a standard CT scan. Further imaging, such as an MRI, might be necessary.
Chronic Subdural Hematoma: This condition can cause cognitive symptoms and may not always be apparent on a CT scan, especially if it is chronic and small.
Infectious or Inflammatory Conditions: Conditions like neurosyphilis, Lyme disease, or multiple sclerosis can cause cognitive symptoms and are important to rule out due to their potential for serious consequences if left untreated.

Frontotemporal Dementia: This is a group of brain disorders caused by cell degeneration in the brain's frontal and temporal lobes, leading to changes in personality, behavior, and language, but it can also present with memory issues.
Korsakoff Syndrome: A brain disorder usually associated with heavy, long-term alcohol consumption, leading to memory problems, but it can be considered in the differential for unexplained memory loss.
Celiac Disease: In rare cases, celiac disease can cause neurological symptoms, including cognitive impairments, due to malabsorption of essential nutrients.