We present a unified multimodal dialog platform for the remote assessment and monitoring of patients' neurological and mental health. Tina, a virtual agent, guides participants through an immersive interaction wherein objective speech, facial, linguistic and cognitive biomarkers can be automatically computed from participant speech and video in near real time. Furthermore, Tina encourages participants to describe, in their own words, their most bothersome problems and what makes them better or worse, through the Patient Report of Problems (PROP) instrument. The PROP captures unfiltered verbatim replies of patients, in contrast with traditional patient reported outcomes that typically rely on categorical assessments. We argue that combining these patient reports (i.e., what they say) with objective biomarkers (i.e., how they say it and what they do) can greatly enhance the quality of telemedicine and improve the efficacy of siteless trials and digital therapeutic interventions.