Case Report and Case Series

A case report is a structured description of what happened to a single patient; a case series is the same for a small group, usually consecutive patients sharing an exposure or an outcome. Neither has a comparison group, so neither can produce a rate, a risk or a relative measure. What they produce is existence proof and detail, and dechallenge with rechallenge, where a problem resolves on stopping and returns on restarting, is the strongest evidence a single case can carry.

Their value is signal detection rather than confirmation. Recognition of thalidomide embryopathy began with a 1961 letter describing a cluster of limb malformations, long before any formal study existed. Pharmacovigilance still works this way at scale, with regulatory databases fed by individual reports that become interpretable once a pattern accumulates, and in the peptide market small clusters of published cases have been the first description of infections traced to non-sterile preparation.

A case report shifts a decision by establishing that something is possible and supplying detail a database entry lacks. It cannot tell you how often it happens, whether the drug caused it, or whether the patient would have done worse untreated. The honest move is to design a study rather than change practice, unless the event is rare, severe and biologically coherent.

The abuse is constant: a published case report used as proof of efficacy for a compound with no controlled data at all. A report of improvement after treatment is a testimonial with a digital object identifier attached, since it says nothing about what would otherwise have happened, and conditions that fluctuate or regress toward the mean generate such reports reliably.