Category: F20 F21 F22 F23 F24 F25 F28 F29
F28 — Other nonorganic psychotic disorders: facilitator sheet
Teaching objective
The classification question F28 answers is: "is there a genuinely nonorganic psychotic picture, observed in enough detail, that clearly does not fit F20, F21, F22, F23, F24, or F25, but that can still be described as a specific presentation in its own right?" F28 requires positive, specific information about an atypical picture — it is not a shortcut for an unclear or under-observed case.
Choose material
Worked example · Case: Eight months of one consistent, isolated feature · Case: Persistent, but no delusion at all · Case: Unusual, but only six weeks in
Worked example
Show scenario
Grace, 58, has for the past eight months had persistent auditory hallucinations (hearing her late husband's voice offering reassurance) without ever developing delusions, thought disorder, negative symptoms, or a mood episode. A full medical work-up and substance history are unremarkable, and the pattern has remained essentially unchanged and clearly described across eight months of follow-up.
Reveal step 1
Step 1 — Check organic and substance causes: a full medical work-up and substance history are unremarkable, reasonably excluding these explanations.
Reveal step 2
Step 2 — Check each F20-F25 category in turn: no delusions or thought disorder for F20; no diffuse trait pattern for F21; no single fixed delusion for F22; no acute onset/brief course for F23; no relational induction for F24; no mood episode for F25.
Reveal step 3
Step 3 — Check whether enough is known to describe a specific picture: yes — eight months of consistent, well-documented, isolated persistent hallucinations.
Reveal step 4
Step 4 — Check observation adequacy: eight months is ample time to reasonably exclude the other categories rather than simply being an early or unclear presentation.
Reveal step 5
Conclusion — F28 is best supported: a confirmed nonorganic, well-described, atypical psychotic picture that does not fit F20-F25.
Comparison points
F28 is distinguished from F29 by the amount and specificity of information available: F28 is used when enough is known to describe a real, specific, atypical picture that clearly doesn't fit F20-F25; F29 is used when a psychosis is confidently nonorganic but there simply is not enough information available to describe it more specifically, even as an atypical picture. F28 is distinguished from F20-F25 by having been checked against each of those categories' criteria and not matching any of them, rather than by symptom severity or drama.
Misconception prompt
Reaching for a residual category (F28/F29) instead of doing the classification work: "This case doesn't obviously fit a named category, so it must be 'other' or 'unspecified.'"
Ask the class why this reasoning fails before revealing the explanation below.
Reveal why it fails
F28 and F29 are the least informative categories in the block, and using them prematurely wastes the classification work the more specific categories are designed to capture. F28 specifically requires enough detail to describe a real atypical picture; F29 specifically requires that this level of detail genuinely is not available. Neither is a shortcut for 'I haven't checked the other categories yet' or 'this seems unusual.'
Discussion prompts
Prompt 1
What is the key difference between F28 and simply saying a case is 'confusing' or 'atypical'?
Prompt 2
Why does F28 require adequate observation time before it can be applied?
Prompt 3
Name the two conditions that must both be true before F28 is the best-supported answer.
Summary
A confirmed nonorganic psychotic picture, observed in enough detail to describe specifically, that clearly does not fit F20 through F25.