Over the past seven months, friends of Diego, a 23-year-old graduate student, have noticed a gradual but marked change. He has become increasingly difficult to follow in conversation, often trailing off mid-sentence or shifting between unrelated topics without clear connection. He has stopped attending lab meetings and rarely leaves his apartment, and when friends visit, he shows little emotional expression even when discussing topics that used to excite him, like his thesis research. For the past two months, Diego has expressed a fixed belief that his advisor and several classmates are secretly monitoring his research through his laptop camera; he has covered the camera with tape and refuses to bring his laptop to campus. When a close friend gently pointed out there was no evidence for this, Diego did not become defensive or reconsider -- he calmly explained that the absence of evidence was itself proof of how careful they were being. He has not used any drugs or alcohol during this period, according to his roommate, and there has been no period during these seven months when his mood was notably elevated or depressed beyond generally seeming withdrawn.
Step 1
Read Presenting Info
Read the presenting information above carefully, then continue when ready.
Step 2
Identify Salient Features
Select the features from this vignette that are most diagnostically salient.
Step 3
Identify Possible Families
Which disorder families should be considered as possible explanations for this presentation?
Step 4
Select Relevant Evidence
Select the pieces of evidence that most directly support the leading formulation.
Step 5
Consider Competing Explanations
Select the explanations that are legitimate competing possibilities worth weighing, even if ultimately less supported.
Step 6
Choose Best Formulation
Which formulation is best supported by the full pattern of evidence?
Step 7
Explain Reasoning
In 2-4 sentences, explain which evidence most strongly supports your formulation and why you ruled out the alternatives. Use hedged, professional language.
Step 8
Review Expert Explanation
Compare your reasoning to the expert explanation below.
Expert reasoning
This vignette describes a pattern most consistent with schizophrenia: Diego shows at least three of the five core symptom domains -- disorganized speech, a fixed delusional belief maintained despite direct, reasonable challenge, and negative symptoms (flattened affect, social withdrawal) -- with continuous signs across seven months, exceeding the six-month duration threshold, alongside a marked decline in functioning (withdrawing from lab meetings and social contact). Because psychosis can also appear during mood episodes or during substance use, a careful formulation would confirm the absence of any manic or depressive episode (as described here) and would still want to rule out substance involvement through direct history, even though none is reported by his roommate. The evidence-resistant, calmly held conviction about the laptop camera -- explained away rather than reconsidered when challenged -- is characteristic of a delusion rather than an OCD-type obsession, where insight is more often at least partially preserved. Any real clinical conclusion would require formal assessment and would be stated as a working hypothesis, not a certainty, especially early in a psychotic illness course.