Do premorbid and post-onset cognitive functioning differ between schizophrenia and bipolar disorder? A systematic...

Area of Science:

• Neuroscience
• Psychiatry
• Cognitive Psychology

Background:

• Schizophrenia (SZ) is marked by global cognitive impairment preceding illness onset.
• Bipolar disorder (BD) may lack premorbid deficits, with some studies suggesting reversed deficits.
• Cognitive functioning impairments are documented in both SZ and BD after illness onset.

Purpose of the Study:

• To systematically review and meta-analyze studies comparing premorbid and post-onset global cognitive function between SZ and BD.

Main Methods:

• Searched Medline (PubMed), EMBASE, and PsycINFO for relevant studies.
• Included studies that assessed cognitive functioning in both SZ and BD using the same methods or within the same study.

Main Results:

• SZ patients exhibited significant premorbid (SMD -0.597) and large post-onset (SMD -1.369) cognitive impairments compared to healthy controls.
• BD showed small premorbid intellectual deficits when assessed retrospectively (SMD -0.147) but not prospectively (SMD -0.029).
• BD patients experienced moderate cognitive impairment after illness onset (SMD -0.623).

Conclusions:

• SZ is characterized by significant premorbid intellectual deficits.
• Evidence for premorbid cognitive function in BD is equivocal.
• Both SZ and BD patients show further cognitive decline post-onset, with greater impairment in SZ than BD.