Psoriasis Not a Risk Factor for Cognitive Dysfunction and Dementia

The overlapping genetics between psoriasis and Alzheimer disease is not a risk factor for cognitive dysfunction and dementia development, according to a study published in the Journal of the American Academy of Dermatology.

The study investigated the association between psoriasis and preclinical markers of dementia (ie, cognitive function and magnetic resonance imaging-markers) and the population’s risk for dementia onset in the Rotterdam Study population. The researchers performed a variety of neuropsychological tests on participants with and without psoriasis, to determine cognition, mild cognitive impairment and magnetic resonance imaging-markers, and dementia onset. The study population were examined at various time points.

A psoriasis diagnosis was based on an algorithm that included medical records, prescription data, self-reporting, and skin examinations. The psoriasis population assessment of cognitive function and mild cognitive impairment was determined post-onset only. The study population, which was composed of 318 participants with psoriasis and 9678 participants without psoriasis, was comparable for age and gender distribution. There were observed differences in waist circumference (96.10 vs 93.64 cm, P<.01), obesity (28.33 vs 27.64 average body mass index, P<.01) and hypertension (58.2 vs 52.4%, P=.04) in the psoriasis cohort. 

Objective cognitive impairments were evaluated through mini mental state examination, 15-word verbal learning test, Stroop test, letter-digit substitution task, verbal fluency, and Purdue pegboard test assessments. There was no significant difference in cognitive tests and g-factor scores between the cohorts after adjustment for age, gender, education, and cardiovascular risk factors. Magnetic resonance imaging-marker studies investigated volumetric, microstructural integrity, and focal measures. There were no major differences between the participants with and without psoriasis. Dementia diagnoses were based on a 3-step protocol that includes mini mental state examination, Geriatric Mental Schedule, and in-screen positives by the Cambridge Mental Disorders of Elderly Examination. Follow-up studies identified 810 dementia cases, of which 15 participants were from the psoriasis group. 

Firstly, the number of dementia cases among the psoriasis cohort results in insufficient power to make any firm arguments on psoriasis as a risk factor for dementia development.  Secondly, the composition of the psoriasis cohort (to mild cases) may limit generalizability to more severe cases. Thirdly, the initial psoriasis assessment may have led to outcomes bias.

Taken together, these findings indicate that preclinical markers of dementia are similar between participants with and without psoriasis.

Reference

Pezzolo E, Mutlu U, Vernooij MW, et al. Psoriasis is not associated with cognition, brain imaging markers and risk of dementia: the Rotterdam Study [published online August 6, 2018]. J Am Acad Dermatol. doi: 10.1016/j.jaad.2018.07.046