I was curious about this, too. I found several studies suggesting that the two disorders are often comorbid, but distinct disorders. A significant correlation

I was curious about this, too. I found several studies suggesting that the two disorders are often comorbid, but distinct disorders. A significant correlation was found between measures on the Observer Alexithymia Scale (OAS; subscales are Distant, Uninsightful, Somatizing, Humorless, and Rigid) and schizoid personality disorder. The correlation wasn’t incredible, however - correlation is described as ‘moderate’, and is mostly prominent under the Distant subscale. Alexithymia and schizoid personality disorder have similar features, but unique variance, so while may features of the two overlap, it would be inaccurate to say that they are one and the same. For the sake of comparison, however, the correlation between alexithymia and avoidant personality disorder was shown to also be significant to a similar degree. Alexithymia, rather than being a syndrome of its own, is described more as a trait that can be found within ‘normal’ ranges of personality, so it’s unsurprising that it would have a strong connection with schizoid personality disorder, major depression, and other disorders while also remaining prominent in non-clinical samples. https://www.ncbi.nlm.nih.gov/pubmed/23021894 https://www.ncbi.nlm.nih.gov/pubmed/23021894 Edit: and for what it's worth, I have a family member who probably has alexithymia, but not schizoid. He is a bit on the introverted side, but can be warm, funny, and engaged in one-on-one conversation (so probably not schizoid). However, when he tries to describe his own emotions beyond really basic stuff (angry, sad, happy, etc.), it's like watching a colorblind person try to describe a flower. He clearly has some real difficulties verbally elaborating on his emotional states, even though those states seem clearly present.