Protocol for: Diagnostic trajectories of patients receiving unspecified psychosis-spectrum diagnoses – A retrospective, longitudinal, register-based study in a large UK secondary mental healthcare service from 2007–2024
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Background
Unspecified psychosis-spectrum diagnoses (ICD code F29) are commonly used when the underlying disorder remains uncertain, particularly at first presentation. These diagnoses may persist or later be revised as the clinical picture evolves, yet little is known about their long-term trajectories or implications for treatment and service use in routine mental healthcare.
Objectives
To describe the usage and persistence of unspecified non-organic psychosis (F29) and other non-specific diagnoses, and the time to transition to a specific diagnosis. Secondary objectives are to describe temporal trends in their use, identify demographic and clinical characteristics associated with diagnostic persistence, and characterise treatment patterns, service utilisation, mortality, and discharge across diagnostic groups.
Methods
We will conduct a retrospective longitudinal cohort study using de-identified electronic health-record data from the South London and Maudsley NHS Foundation Trust (SLaM), accessed through the Clinical Record Interactive Search (CRIS) system, between 1 January 2007 and 31 December 2024. The study population will include patients with an ICD-10 psychosis-spectrum diagnosis (F2x.x), substance induced psychotic disorder (or F1x.5), bipolar disorder or affective disorder with documented psychotic symptoms(F32/3.3). Diagnoses will be classified as specific or non-specific according to their ICD-10 category. Primary analysis will examine time from first F29 diagnosis to first subsequent specific psychosis-spectrum or bipolar diagnosis using Cox proportional hazards regression, with discharge from SLaM, death and administrative end of follow-up treated as censoring events. Associations with diagnostic transition will be examined adjusting for age, sex, ethnicity, area-level deprivation, route of service entry, and calendar period. Secondary competing-risk analysis will estimate the cumulative incidence of diagnostic transition using the Aalen– Johansen estimator, treating discharge and death as competing events.
Ethics and Dissemination
CRIS operates under ethical approval from the South Central–Oxford C Research Ethics Committee (23/SC/0257). Project-specific approval was received from the CRIS Oversight Committee as Project 23-095. The study will be reported in accordance with the RECORD extension of the STROBE guidelines. Findings will be disseminated through peer-reviewed publication and will provide evidence on the longitudinal use and refinement of non-specific psychosis-spectrum diagnoses in routine secondary mental healthcare.
