• A recent review of several existing studies highlights how inflammation is related to both Alzheimer’s disease and skin diseases, like psoriasis.
• Inflammation caused by shared cytokines — such as TNF-alpha — is involved in both diseases, possibly linking them to each other.
• People with psoriasis are at a higher risk of developing dementia, and vice versa, but researchers noted there is no precise correlation.

A recent review of existing studies highlights the relationship between Alzheimer’s disease and skin diseases — including psoriasis, skin cancer, and hidradenitis suppurativa. Researchers found that inflammation acts as a driver in all of these diseases, connecting them.

Dementia is a neurological disorder that affects 50 million people worldwide, particularly people of older age. Alzheimer’s disease is the most common subtype of dementia, accounting for about 44 percent of all cases.

Several studies have investigated the relationship between Alzheimer’s disease and skin diseases. The authors of this review set out to summarize the findings so that neurologists and dermatologists are fully informed.

Inflammation as a Driver of Alzheimer’s Disease and Psoriasis

Psoriasis is a chronic inflammatory skin condition that causes scaly plaques to form. It affects 125 million people around the world — and 8 million people in the United States alone. While the main effects of the disease appear on the skin, psoriasis is also associated with other complications, such as mental disorders, cardiovascular disease, and other immunological diseases.

The connection between dementia and psoriasis has been previously studied, and while the exact link is not known, researchers believe inflammation is to blame. In psoriasis, inflammatory mediators known as cytokines are responsible for activating the immune system. Some of these cytokines are shared between psoriasis and Alzheimer’s disease, connecting them through inflammation.

One cytokine — tumor necrosis factor alpha (TNF-alpha) — is known to play a role in both diseases. Treating psoriasis with TNF inhibitors — biologics that block TNF-alpha — improves skin disease. These medications also improve cognitive function in Alzheimer’s disease. In fact, one study found that treating people with psoriasis with TNF-alpha blockers lowered their risk of developing Alzheimer’s disease compared to those who did not receive the treatment.

The Role of Genetics

Genetics may also play a role in the connection between the two diseases. One protein — apolipoprotein E (APOE) — is known to be strongly associated with Alzheimer’s disease and can also be a risk factor for psoriasis.

APOE acts as a cholesterol carrier, which affects the formation of plaques that form on the brain in Alzheimer’s disease. A large study of people with psoriasis and those without found that certain versions of the APOE gene influence the risk of developing the skin disease. This connection potentially links the two diseases.

Risks of Developing Psoriasis and Alzheimer’s Disease

Research has found that people with psoriasis are 10 percent to 25 percent more likely to develop dementia. Researchers also have found that those with dementia have an increased risk of developing psoriasis. However, one study did find that having psoriasis protects against dementia.

The review authors also noted that studies have found that people with psoriasis are at a higher risk for developing issues concentrating, solving problems, and remembering information — all signs of early dementia. Although there is an increased risk of developing psoriasis and Alzheimer’s disease, the authors note that there is not an exact correlation. More research is needed to confirm this relationship.