When Restrictive Eating Masks a Rare Immune-Driven Neuropsychiatric Syndrome

A nine-year-old girl walked into a specialty outpatient eating disorder treatment center with a presentation that looked, on the surface, entirely familiar to the clinicians there: restrictive eating, an intense fear of weight gain, disturbed body image, and obsessive-compulsive behaviors that seemed designed to compensate for whatever she did eat. Her team diagnosed other specified feeding or eating disorder, in the atypical anorexia nervosa subtype, and began family-based treatment, the best-evidenced approach for adolescent eating disorders, in which parents take charge of refeeding their child. Yet what happened next has prompted a new case report from researchers at Stanford University School of Medicine, published in the Journal of Eating Disorders, that asks an uncomfortable question: how often are eating disorder symptoms actually the visible edge of something else entirely?

Despite stabilizing weight and improving nutrition through family-based treatment, the girl deteriorated. Her functional decline was severe and progressive, and it did not track with her nutritional status. That mismatch, the Stanford team argues, should be a signal that clinicians cannot afford to ignore. She was eventually evaluated at an immune behavioral health clinic and diagnosed with pediatric acute-onset neuropsychiatric syndrome, or PANS, a rare and heterogeneous condition that remains poorly understood at the intersection of child psychiatry, immunology, and eating disorder medicine.

PANS is defined clinically rather than by a biomarker. It is characterized by an abrupt, dramatic onset of obsessions, compulsions, and/or food restriction, accompanied by at least two additional acute-onset neuropsychiatric symptoms, which can range from anxiety and emotional lability to irritability, aggression, developmental regression, deterioration in school performance, sensory or motor abnormalities, and sleep disturbance. The key word is acute: symptoms appear seemingly overnight, in a way that is qualitatively different from the gradual unfolding of typical psychiatric illness. The syndrome sits within a broader family of post-infectious and immune-mediated neuropsychiatric conditions, and its diagnosis is currently exclusionary, meaning clinicians must rule out better-established disorders before attributing symptoms to PANS.

That exclusionary status creates a diagnostic trap. The core symptoms of PANS overlap heavily with obsessive-compulsive disorder, tic disorders, and eating disorders, all of which are common and well-characterized in children. A child who suddenly stops eating and develops obsessive fears around food can look indistinguishable from a child with early anorexia nervosa, particularly when body image concerns are present. The Stanford case is notable precisely because the girl did show body image disturbance and fear of weight gain, features that are not typically emphasized in PANS-related food restriction, which is more often described as driven by contamination fears, choking phobias, or sensory aversions rather than by weight and shape concerns.

The treatment trajectory in the case illustrates why the distinction matters. Family-based treatment, which empowers parents to restore their child’s weight through structured, supportive meals, is highly effective for many children with atypical anorexia nervosa, and indeed this patient did achieve weight stabilization and nutritional improvement. But PANS is thought to involve immune and inflammatory mechanisms, and neuropsychiatric symptoms driven by those processes are not expected to remit with refeeding alone. When a child continues to decline functionally despite adequate nutrition and evidence-based eating disorder care, the case report suggests, clinicians should widen their differential rather than assume the eating disorder is simply treatment-resistant.

The Stanford authors propose a set of clinical red flags that might prompt eating disorder specialists to consider PANS: a combination of acutely onset restrictive eating, body image disturbance occurring before puberty, and progressive functional impairment or developmental regression despite weight restoration. Each element is significant. Acute onset distinguishes PANS from the insidious course typical of anorexia nervosa. Prepubertal body image disturbance is unusual, since weight and shape concerns classically intensify with pubertal development. And failure to improve, or outright regression, after nutritional restoration runs counter to the expected course of a primary eating disorder, in which renourishment typically produces marked cognitive and behavioral improvement.

Management of the girl’s care ultimately required a carefully staged transition. She moved from the eating disorder clinic, where family-based treatment had addressed the atypical anorexia nervosa, to an immune behavioral health clinic and a sleep clinic, which together managed the remaining neuropsychiatric symptoms of PANS. The handoff was gradual rather than abrupt, reflecting the reality that many patients with overlapping presentations need both nutritional rehabilitation and immune-informed psychiatric care simultaneously. The authors highlight this coordination as a central lesson: specialty clinics are organized around diagnoses, but patients do not always respect those boundaries, and triage across clinics can determine whether a child receives the right treatment at the right time.

The broader scientific context remains contested. PANS, and its post-infectious predecessor concept PANDAS, or pediatric autoimmune neuropsychiatric disorders associated with streptococcal infection, have been debated within child psychiatry for decades. Proponents point to clinical clusters of sudden-onset symptoms, sometimes following infections, and to emerging work on immune markers and basal ganglia involvement. Skeptics note the absence of a validated biomarker, the heterogeneity of presentations, and the risk of mislabeling ordinary psychiatric illness as an immune condition. Case reports like this one occupy an important middle ground: they do not settle the underlying immunology, but they document real clinical trajectories and give other clinicians concrete patterns to watch for.

What makes this case particularly striking is the body image component. Food restriction in PANS has most often been framed as a fear-based or sensory-driven phenomenon, distinct from the weight and shape preoccupation that defines anorexia nervosa. A child with PANS features who also expresses fear of weight gain challenges that tidy separation and suggests that the two conditions may coexist, or that immune-driven neuropsychiatric illness can generate eating-disorder-like cognitions in some children. Either possibility has implications for assessment: eating disorder clinicians may need to probe more systematically for acute onset, accompanying neuropsychiatric symptoms, and developmental regression when evaluating young, prepubertal patients with restrictive eating.

The Stanford team, led by Megan M. Ruiz Fischer with colleagues including Jennifer L. Derenne, Melissa A. Silverman, Anne Claire Grammer, and Brittany Matheson, is careful to frame the report as a starting point rather than a conclusion. A single case cannot establish prevalence, causation, or treatment guidelines, and the authors note that little is known about the crossover between eating disorders and PANS, with minimal existing guidance on diagnostic and treatment considerations for these patients. But the report adds a concrete, well-documented example to a sparse literature, and its practical message is likely to resonate far beyond eating disorder specialty centers: when a child’s trajectory defies expectations, when nutrition improves but the child keeps slipping, the diagnosis on the chart may be incomplete. For families navigating the frightening territory of sudden psychiatric change in a young child, that message, that deterioration despite treatment deserves a fresh diagnostic look rather than blame or resignation, may be the most important takeaway of all.

Subject of Research: Diagnostic overlap between atypical anorexia nervosa and pediatric acute-onset neuropsychiatric syndrome (PANS) in children

Article Title: Anorexia nervosa or pediatric acute-onset neuropsychiatric syndrome? A case report

Article References: Ruiz Fischer, M. M., Derenne, J. L., Silverman, M. A., Grammer, A. C., & Matheson, B. (2026). Anorexia nervosa or pediatric acute-onset neuropsychiatric syndrome? A case report. Journal of Eating Disorders. https://doi.org/10.1186/s40337-026-01783-8

Image Credits: AI Generated

DOI: 10.1186/s40337-026-01783-8

Keywords: PANS, pediatric acute-onset neuropsychiatric syndrome, anorexia nervosa, atypical anorexia nervosa, eating disorders, family-based treatment, obsessive-compulsive symptoms, food restriction, child psychiatry, immune-mediated neuropsychiatric illness, case report, diagnostic overlap