Characterizing and dating the onset of symptoms in psychotic illness: the Symptom Onset in Schizophrenia (SOS) inventory

Prodromal symptoms, including disturbances of perceptions, beliefs, cognition, affect, and behavior, are often the first symptoms of schizophrenia. Little is understood about the initial, prodromal stage of schizophrenia, despite the compelling research and clinical need. The development and psychometric properties of a new, time-efficient instrument to characterize and date the initial symptoms of a psychotic illnesses, the Symptom Onset in Schizophrenia (SOS) scale, is described in this paper. The SOS rates the presence and dates the onset of 16 general prodromal, positive, negative, and disorganizational symptoms, as well as a clinician, family, and patient global rating of onset of illness. Inter-rater reliability for the presence of each symptom in 35 patients with schizophrenia, schizoaffective, or schizophreniform disorder was good to excellent, with kappa coefficient >0.7 for 12 items, and >0. 5 for all items. Agreement on symptom duration was good to excellent for individual items (ICC=0.7-1.0) and for global rating of duration of illness (ICC=0.97). Our data indicate that the SOS is a reliable, valid, time-efficient tool useful to retrospectively assess the onset of schizophrenia and related psychotic disorders. Further study is underway to evaluate other psychometric properties of the SOS, including test-retest reliability and predictive validity.