The aim of the study will be to compare the efficacy of daily plasma exchange (PLEX) versus alternate-day PLEX in achieving a favorable functional outcome in children with autoimmune encephalitis.

The study population will be divided into two groups, the first group will perform PLEX on consecutive days and the second one will perform it every other day. Then, A Favorable functional outcome measure defined as modified Rankin Scale (mRS) score ≤ 2. The mRS will be assessed by a blinded assessor at the end of the sessions to determine which method has superior efficacy in treatment of autoimmune encephalitis.

This will be a Prospective, randomized, open- label, parallel-group, center trial, which will include enough number of children admitted at Pediatric Intensive Care Unit (PICU) of Menoufia university Hospital with autoimmune encephalitis from August 2026 to February 2027.

Grouping :

The study population will be divided into two groups:

1. Daily PLEX Group (Arm A):

   This group will perform PLEX on consecutive days (e.g., Day 1, 2, 3, 4, 5) for 5 sessions; up to 7 sessions allowed.

2. Alternate-Day PLEX Group (Arm B):

This group will perform PLEX every other day (e.g., Day 1, 3, 5, 7, 9) for 5 sessions; up to 7 sessions allowed.

All patients in this study will be subjected to:

A- Demographic and clinical data Collection:

• Patient demographics: age, sex, Wt., Ht., and body mass index (BMI).
• PLEX parameters: date/time of each session, exchanged volume, replacement fluid, anticoagulation used and immediate complications if any.

B- Full clinical examination will be done including vital signs (HR, RR, BP, temperature), Pediatric Glasgow Coma Scale to assess consciousness level and neurological examination.

C- Investigations will be done including the following:

Laboratory Analysis: CBC, CRP, Electrolytes, calcium level, blood culture, urea, creatinine, ALT, AST, procalcitonin, coagulation profile and D-dimer level.

Radiological: Chest X ray, Brain CT, MRI and EEG if they needed. Intervention and Monitoring

Plasma Exchange Procedure (both arms):

A- Access: Central venous catheter (size appropriate for age and weight) or existing dialysis catheter.

B- Exchange volume: 1-1.5 plasma volumes per session (age/weight-adjusted - typical formula: plasma volume = 0.07 × weight in kg × (1 - hematocrit)).

C- Replacement fluid: 5% human albumin as first choice; fresh frozen plasma (FFP) may be used if clinically indicated (bleeding, coagulopathy), or combination as per local protocol.

D- Anticoagulation: Regional citrate anticoagulation or systemic heparin according to institutional practice; monitor ionized calcium if citrate used.

E- Monitoring: Vital signs pre-, intra-, and post-procedure; electrolytes, coagulation profile and calcium level as clinically indicated.

F- Number of sessions: Up to 5 sessions recommended; clinicians may extend to 7 sessions if inadequate clinical response.

Inclusion Criteria:

• Childern diagnosed as autoimmune encephalitis according to Cellucci et al., 2020; acute/subacute onset (<3 months) of encephalopathy with at least one of: new focal CNS findings, seizures, CSF pleocytosis, MRI suggestive of encephalitis, and supportive antibody testing when available.
• Autoimmune encephalitis cases indicated clinically for PLEX as determined by the treating team (e.g., severe disease, refractory to steroids/IVIG or as part of first-line combination therapy).

Exclusion Criteria:

• Hemodynamic instability not amenable to plasma exchange.
• Severe coagulopathy uncorrectable prior to PLEX (INR >2 despite correction, platelets <50,000/µL unless corrected).
• Contraindications to central venous access placement.
• Enrollment in another interventional trial that would interfere with the outcomes.