Learn the symptoms in the four stages of CTE

This graphic shows the classic features of CTE in the brain of Aaron Hernandez.DON VEITCH

Aaron Hernandez’s lawyers, citing Boston University, announced Thursday that the former New England Patriots star suffered from chronic traumatic encephalopathy.

A statement released by the BU CTE Center stated that Hernandez was found to have Stage 3 CTE, with Stage 4 being the most severe.

According to a 2012 BU study, CTE begins with simple symptoms such as headaches and difficulty concentrating, but as the disease progresses, other, much more worrying conditions appear.

Stage I

Early on, symptoms include headaches as well as loss of attention and concentration.

Stage II

In stage II, those with CTE find themselves suffering from depression or mood swings, explosivity, and short term memory loss, in addition to Stage I symptoms. Although less common, other Stage II signs include: executive dysfunction, language difficulties, impulsivity, and the potential for suicide.

Stage III

“Executive dysfunction, memory loss, explosivity, and difficulty with attention and concentration” begin when those with CTE reach Stage III. Additionally, those with Stage III CTE also frequently develop “depression or mood swings, visuospatial difficulties, and aggression.” Headaches, apathy, impulsivity, and “suicidality” symptoms have also been noted, although to a lesser extent. According to BU, 75 percent of the people studied with Stage III CTE were considered “cognitively impaired.”

Stage IV

The most severe stage of CTE, those in Stage IV suffer from executive dysfunction and memory loss initially and then develop severe memory loss with dementia. Additionally, researchers found that most of the people studied with Stage IV also developed “a profound loss of attention and concentration, executive dysfunction, language difficulties, explosivity, aggressive tendencies, paranoia, depression, gait and visuospatial difficulties.”

According to BU, less common symptoms include impulsivity, dysarthria, and parkinsonism, and at least 31 percent of those studied were at suicidal at some point.

The study also explains that the most common causes of death for those with CTE are respiratory failure, cardiac disease, suicide, overdose, and symptoms associated with end-stage dementia and malignancy.