After NMDA receptor encephalitis, the illness changes shape rather than ending

Design

Cross-sectional study with 1:1 propensity-matched healthy controls and normative modelling of MRI

Population

70 patients with post-acute NMDA receptor encephalitis, median 22.2 months from onset, and 70 matched controls

Primary outcome

Morphological brain complexity and residual clinical symptoms

Effect

Residual symptoms in 47/70 (67%): memory dysfunction 61%, psychiatric symptoms 36%, with stronger morphological alteration in those affected

Seventy patients with post-acute NMDA receptor encephalitis were assessed a median of 22 months after onset and matched one-to-one with healthy controls. They had improved enormously — median modified Rankin Scale 5 at peak illness to 1 — and yet 47 of the 70 still had residual symptoms on the Clinical Assessment Scale for Autoimmune Encephalitis. Memory dysfunction was present in 61 per cent and psychiatric symptoms in 36 per cent.

The important clinical observation is the shift. At peak illness the psychiatric picture was psychosis-dominant; in the post-acute stage it was affective-dominant. A patient who presented with agitation, delusions and catatonia returns, two years on, with depression and blunted drive — and is easily read as having a new primary mood disorder rather than a residue of the encephalitis.

MRI showed reduced morphological complexity in both hippocampi and a fronto-cingulo-temporal cluster, and the patients with persistent symptoms had the stronger structural alterations. That is an imaging marker at the group level, not a test for an individual. What it supports is a structured follow-up clinic rather than discharge once the immunotherapy course ends.

• Ask directly about memory at every post-encephalitis review; it is the commonest residue and patients rarely volunteer it.
• Treat new affective symptoms in this group as part of the illness course until proven otherwise.
• Arrange formal neuropsychological testing rather than relying on a bedside cognitive screen.
• Set expectations at discharge: good functional recovery is compatible with persistent cognitive and affective morbidity.
• Keep these patients in a named follow-up pathway; the deficits emerge after the acute service has stepped back.

Why it matters

The patient who recovers well from the acute illness is the one most likely to be discharged with the part that lasts.

Don't overread it

Fractal dimensionality is a research imaging measure; it does not yet identify which individual will have persistent symptoms.

The statistics, in plain English

This is cross-sectional imaging at one time point, so the structural differences cannot be dated — the study cannot say whether reduced complexity preceded, accompanied or followed the persistent symptoms. The comparisons between symptomatic and asymptomatic patients are within a sample of 70 and were not pre-registered as the primary question, so the effect sizes (t −2.65 for psychiatric symptoms, t −3.98 for memory) describe a consistent gradient rather than a validated threshold.

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