Introduction Cognitive dysfunction is present in the prodromal phase of Huntington Disease (HD) before motor diagnosis is given. In order to obtain an evaluation of the patients' global cognitive function, complex batteries of exams are needed. For this purpose, the Mini Mental State Exam (MMSE) is the screening test most frequently used. On the other hand, the Montreal Cognitive Assessment (MoCA) is a recent screening test with higher sensitivity for mild cognitive impairment. It has bean applied for the detection of the earliest cognitive impairments in patients with HD.

Objective To compare the MMSE with the MoCA in identifying cognitive deficits in prodromal and early stages of HD.

Methods The MMSE and the MoCA were performed in 37 patients with genetic diagnosis of HD regularly evaluated in the Neurogenetic Consultation of the Coimbra's University Hospital; as well as in 40 control subjects with no neurodegenerative pathology, using age, gender and education as comparison factors in the selection criteria.

Results Both groups (subjects with HD and control subjects) showed no differences in the distribution of the demographic characteristics. The MMSE and MoCA's total scores showed lower values in the HD group (p=0.002 and p=0.003 respectively). Samples' description according to educational level showed differences between the two groups in the MMSE scores only, for an education lower or equal to 11 years. With the cut-offs determined to the Portuguese population, the MoCA presented a superior sensitivity to detect cognitive decline among HD patients in comparison to the MMSE (64, 9% vs 21, 6%; p<0.001). Receiver Operating Characteristics curves analysis registered significant statistic results only in the MoCA, concerning Visual-Spacial, Language and Executive Function/Attention areas (p=0.01, p=0.039 and p=0.018, respectively).

Conclusions According to the cut-offs established for the Portuguese population, the MoCA is a brief screening test with higher sensitivity in the detection of cognitive impairments related to Huntington's Disease, when in comparison to the MMSE, requiring tasks inherent to cerebral areas characteristically affected in this disease. Due to the fact that it evaluates certain cerebral domains, such as the Executive/Attention Function, it reveals itself more appropriate for the detection of the mild cognitive impairment in Huntington's disease patients, and should therefore be used instead of the MMSE.