A case of autoimmune encephalitis with autoimmune gastritis presenting as refractory hyponatremia

Abstract

Background

The coexistence of autoimmune encephalitis (AE) and autoimmune gastritis (AIG) is exceedingly rare, and their simultaneous presentation often manifests as refractory hyponatremia, which can be easily overlooked. This report describes a case of anti-leucine-rich glioma-inactivated 1 (LGI1) antibody-associated AE coexisting with AIG, presenting initially as refractory hyponatremia, aiming to enhance awareness of multisystem autoimmune involvement.

Case presentation

A 77-year-old man presented with a two-month history of poor appetite, fatigue, and drowsiness, which had worsened over the preceding week. He had an 8-year history of psoriasis. Laboratory evaluation revealed profound hyponatremia (serum sodium nadir 109 mmol/L), macrocytic anemia (hemoglobin 88 g/L, mean corpuscular volume 118 fL), and deficiencies of vitamin B12 and iron. Gastroscopy with histopathological examination confirmed the diagnosis of autoimmune gastritis. Due to poor response of hyponatremia to conventional sodium supplementation and the presence of left limb spasms, further diagnostic work-up was pursued. Cerebrospinal fluid analysis tested positive for anti-LGI1 antibodies (titer 1:64), and brain magnetic resonance imaging revealed bilateral hippocampal T2-FLAIR hyperintensity and a T2 hyperintense signal in the pituitary gland, leading to the diagnosis of anti-LGI1 antibody-associated AE complicated by central adrenal insufficiency. Following methylprednisolone pulse therapy, the patient’s serum sodium normalized, left limb spasms resolved, and mental status improved. At the 8-month follow-up, the patient remained clinically stable.

Conclusion

This case highlights that in patients presenting with refractory hyponatremia accompanied by multisystem manifestations, the possibility of coexisting autoimmune diseases such as AE and AIG should be considered. Comprehensive autoimmune antibody screening and neuroimaging are crucial for early diagnosis and timely intervention.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-026-04920-7.

Autoimmune encephalitis (AE) is a distinct category of encephalitis mediated by autoimmune mechanisms. Under certain conditions, autoantibodies produced by the body target healthy brain tissue, leading to a series of clinical symptoms, including refractory hyponatremia and altered mental status. Its incidence is approximately 1 per 100,000 individuals, and the co-occurrence of AE with AIG is exceedingly rare. This report reviews the clinical data and diagnostic workup of a patient presenting with refractory hyponatremia as the primary manifestation of AE concurrent with AIG. It aims to discuss their pathogenic characteristics, thereby enhancing recognition of multi-organ autoimmune involvement and broadening the differential diagnosis of refractory hyponatremia.

Clinical data

General information

The patient is a 77-year-old male admitted on August 15, 2023, due to poor appetite, fatigue, and drowsiness for over 2 months, which had worsened in the preceding week.

History of present illness

Approximately two months prior to admission, the patient presented to an external hospital with poor appetite, fatigue, and drowsiness. Laboratory tests revealed hyponatremia (Serum Na⁺: 108.8 mmol/L). He was hospitalized and received sodium supplementation for 6 days. Upon discharge, his serum Na⁺ had improved to 129.4 mmol/L, and his appetite had somewhat improved. One week before the current admission, his symptoms of poor appetite, fatigue, and drowsiness worsened, accompanied by involuntary limb spasms. A repeat test showed serum sodium of 109 mmol/L, leading to his admission to our department with a diagnosis of “hyponatremia.”

Past medical history

He has a 10-year history of hypertension, without regular medication use or blood pressure monitoring. He also has an 8-year history of psoriasis, treated with oral Chinese herbal medicine with poor disease control.

Family, personal, and marital/obstetric history

Unremarkable.

Physical examination

Vital signs were stable with a BMI of 20.10 kg/m². Neurological examination findings are summarized in Table 1. Additional findings included pale conjunctiva, scattered psoriatic plaques on the limbs, and mild epigastric tenderness without rebound or edema.

Table 1.

Structured neurological examination findings

Domain	Findings
Cognition	Patient was drowsy but arousable; oriented to person and place, disoriented to time; impaired sustained attention and psychomotor slowing. Formal cognitive testing (MMSE, MoCA) was not feasible due to fluctuating alertness. Deficits were consistent with a mixed pattern of metabolic encephalopathy and early limbic dysfunction.
Cranial nerves	Unremarkable.
Motor	Normal bulk and strength (5/5) in all extremities; mildly increased tone in left upper and lower limbs. Recurrent, brief (3–10 s), stereotyped dystonic posturing spasms involving left arm and leg, occurring approximately 10–15 times per hour (100–150 episodes daily) without impairment of awareness. No consistent triggers were identified, and no falls occurred during episodes.
Sensory	Intact to light touch and pinprick throughout.
Coordination	Mild left-sided dysmetria on finger-to-nose testing.
Reflexes	Deep tendon reflexes symmetric (2+) throughout; flexor plantar responses bilaterally; no pathological reflexes.
Gait	Not formally assessed due to drowsiness.

Additional findings included pale conjunctiva, scattered psoriatic plaques on the limbs, and mild epigastric tenderness without rebound or edema.

Investigations

Laboratory tests revealed the following: WBC 8.3 × 10^9/L; NE% 85.80%; Hb 88.00 g/L; MCV 118.00 fL; PLT 143.0 × 10^9/L. Biochemistry showed total protein 53.1 g/L, albumin 27.5 g/L, normal renal function, fasting blood glucose 6.25 mmol/L, serum Na + 110.0 mmol/L, serum K + 3.51 mmol/L, and plasma osmolality 251 mmol/L. Tumor markers were normal except CA-125 (46 U/mL). Thyroid function tests were normal. Pituitary–thyroid and pituitary–gonadal axes were intact: TSH, FT3, FT4 ,FSH, LH 5, PRL all within normal limits, indicating selective impairment of the corticotroph axis. A morning serum cortisol was profoundly low (< 1.1 nmol/L) with a concomitantly low ACTH (2.1 pg/mL), confirming central adrenal insufficiency. An ACTH stimulation test was not performed due to the urgent clinical presentation (severe symptomatic hyponatremia [serum sodium 109 mmol/L] requiring immediate treatment); the diagnosis was based on the characteristic biochemical profile and the patient’s excellent response to glucocorticoid replacement. The erythrocyte sedimentation rate was elevated at 58 mm/h, while C-reactive protein was 5 mg/L. CT imaging revealed localized emphysema in the left upper lobe, micro-nodules in both lower lobes, multiple hepatic cysts, and scattered lacunar infarcts in the bilateral corona radiata (Fig. 1).

Fig. 1.

(a) Micro-nodules observed in the lower lobes of both lungs; (b) Multiple cysts within the liver; (c) Scattered lacunar infarcts in the bilateral periventricular white matter

Diagnostic and therapeutic course

The patient presented with severe hyponatremia. After admission, 3% hypertonic saline was administered to correct the electrolyte imbalance. On the first day, a total of 18 g of sodium chloride was supplemented. A recheck the following day revealed a serum sodium level of 111 mmol/L, prompting continued supplementation with serum sodium monitoring every 4 h. Given his active psoriasis, gastrointestinal symptoms, macrocytic anemia, and mental abnormalities, further investigations were pursued. Autoimmune antibody testing showed: ANA 1:320, anti-Jo-1 antibody positive (+), and anti-centromere antibody positive (+). Serum vitamin B12 was significantly low at 73.33 pg/ml (reference range: 183–822 pg/ml), and serum iron was decreased at 6.3 µmol/L (reference range: 11.6–31.3 µmol/L). Pepsinogen I was markedly reduced to 7.016 ng/ml (reference range: 70–240 ng/ml), with pepsinogen II at 6.058 ng/ml, resulting in a PGI/PGII ratio of 1.16 (Table 2) .The 14 C-urea breath test was negative for H. pylori. Anti-gastric parietal cell antibody IgG was positive (+). Gastroscopy revealed an “inverse pattern of gastric atrophy,” characterized by mild inflammation in the antral mucosa and moderate atrophy in the oxyntic gland mucosa of the gastric body (Figs. 2, 3, 4 and 5). Further gastric pH monitoring, conducted over a total duration of 5 h, 21 min, and 48 s, consistently showed intragastric pH values above 4 (Fig. 6).

Table 2.

Key laboratory findings

Test	Result	Reference Range
24-hour urinary sodium	317.4 mmol/24 h	40–220 mmol/24 h
Morning cortisol	< 1.1 nmol/L	138–635 nmol/L
ACTH	2.1 pg/mL	7.2–63.3 pg/mL
CSF anti-LGI1 antibody	Positive (1:64)	Negative
Anti-parietal cell antibody IgG	Positive	Negative
Hemoglobin	88 g/L	130–175 g/L
Vitamin B12	73.33 pg/mL	183–822 pg/mL
ANA	1:320	< 1:80
Pituitary function tests (TSH, FT3, FT4, FSH, LH, PRL)	Normal	–

Fig. 2.

Demonstrates gastric atrophy involving the fundus and body, with the gastric antrum spared

Fig. 3.

(Antrum) Biopsy tissue: mild chronic mucosal inflammation

Fig. 4.

(Midbody) Biopsy tissue: moderate chronic mucosal inflammation, mild intestinal metaplasia, and moderate glandular atrophy

Fig. 5.

(Fundus) Biopsy tissue: moderate chronic mucosal inflammation, mild intestinal metaplasia, and moderate glandular atrophy

Fig. 6.

Dynamic gastric pH Monitoring: gastric pH monitoring was conducted for a total duration of 05:21:48, during which the gastric pH remained consistently above 4

These comprehensive findings established a definitive diagnosis of autoimmune gastritis (AIG, Type A). Consequently, while continuing sodium supplementation, treatment was initiated with iron, vitamin B12, and folic acid to correct the anemia.

Despite ongoing sodium supplementation, on day 5 of hospitalization, serum sodium gradually increased to 117 mmol/L. At this time, the patient’s drowsiness and fatigue showed partial improvement; however, the left limb spasms remained frequent, occurring multiple times per hour. This dissociation suggested that while global encephalopathic symptoms (drowsiness, fatigue) were partially responsive to sodium correction, the focal motor symptoms (left limb spasms) persisted independently of sodium levels. Subsequently, after initiating methylprednisolone pulse therapy (1000 mg/day for 3 days), the limb spasms completely resolved by the third day of immunotherapy. Mental status and cognitive function continued to improve over the following weeks, paralleling the immunomodulatory treatment rather than sodium normalization. Repeat laboratory tests revealed a hemoglobin level of 98 g/L and a serum sodium level of 117 mmol/L, indicating persistent severe hyponatremia. This suggested that AIG alone was insufficient to explain the entire clinical picture.

Brain MRI was subsequently performed. Axial T2-FLAIR images showed patchy areas of high signal intensity within the bilateral hippocampi. Corresponding T2-weighted images confirmed bilateral hippocampal swelling and increased T2 signal. Sagittal and coronal pituitary MRI sequences revealed a small focal area of T2 hyperintensity within the pituitary gland (Fig. 7). This finding may suggest autoimmune inflammation (e.g., lymphocytic hypophysitis) in the appropriate clinical context; however, it should be interpreted with caution, as such signal abnormalities are non-specific. Differential diagnoses include incidental microadenoma, age-related changes, or partial volume artifact. In this patient, the presence of biochemical evidence of central adrenal insufficiency (low ACTH and cortisol) lends support to the possibility that this imaging finding represents the structural correlate of hypothalamic-pituitary axis dysfunction. Nevertheless, further confirmation would require dynamic endocrine testing (e.g., ACTH stimulation test) and dedicated pituitary imaging with contrast enhancement, which were not performed due to the patient’s clinical stability and refusal of additional investigations. Importantly, this interpretation remains speculative in the absence of contrast-enhanced imaging and dynamic endocrine testing. Lumbar puncture demonstrated an opening pressure of 101 mmH₂O, with normal cerebrospinal fluid (CSF) routine and biochemical analysis. Antibody testing was performed using a commercial cell-based assay (Euroimmun, Lübeck, Germany) according to the manufacturer’s standard operating procedures. The testing laboratory is accredited under ISO 15189. Anti-LGI1 antibodies were detected in the cerebrospinal fluid (CSF) at a titer of 1:64, while serum testing was negative, demonstrating a ‘CSF-only’ positivity pattern. The turnaround time for these results was 5 working days. While serum detection of anti-LGI1 antibodies is more common than CSF detection, a CSF-positive/serum-negative pattern has been described in approximately 17–22% of patients with anti-LGI1 encephalitis when using commercial cell-based assays [1]. Therefore, although this pattern is less frequent, it remains compatible with the diagnosis in the appropriate clinical context. The cell-based assay employed (Euroimmun) has demonstrated high specificity for anti-LGI1 antibody detection. In the appropriate clinical context—characterized by FBDS-like limb spasms, refractory hyponatremia, and bilateral hippocampal abnormalities on MRI—a positive CSF antibody finding is sufficient to establish the diagnosis, even in the absence of serum confirmation [2]. Other neuronal surface antibodies, including anti-NMDAR, anti-GABABR, and anti-CASPR2, were systematically tested and were negative in both CSF and serum. Electroencephalography (EEG) showed mild non-specific background slowing with slightly increased fast-wave activity interictally, and no ictal epileptiform discharge was observed during a recorded episode of left limb spasm (Fig. 8).

Fig. 7.

a Axial T2WI FLAIR MRI of the brain showing patchy high signals in the bilateral hippocampus. b Axial T2WI MRI of the brain showing bilateral hippocampal swelling with increased signal intensity. c Sagittal MRI of the pituitary gland. d Coronal MRI of the pituitary gland. Small patchy areas of high signal intensity are observed on T2-weighted images within the pituitary gland (as indicated by the red arrow)

Fig. 8.

Electroencephalogram (EEG) findings. Interictal period: showing mild background slowing with slightly increased fast-wave activity. Ictal period: recorded during a clinical episode of left limb spasm; no electrographic seizure discharge or epileptiform activity is observed

The final diagnosis was revised to definitive anti-LGI1 antibody-associated AE co-existing with AIG.

Treatment

Prior to initiating immunotherapy, baseline screening showed no abnormalities in hepatitis panels, EBV/CMV serology and PCR, T-SPOT.TB, or PPD test. The patient received intravenous methylprednisolone pulse therapy (1000 mg/day for 3 days, followed by 500 mg/day for 3 days, and then 250 mg/day for 3 days). This was succeeded by intravenous methylprednisolone at 60 mg/day for 2 weeks. Throughout treatment, blood glucose and blood pressure were closely monitored, with concomitant supplementation of potassium, gastric protectants, and calcium, alongside symptomatic management. The patient’s condition improved significantly, with resolution of limb spasms, improved mental status, and normalization and subsequent stability of serum sodium levels. Upon discharge, the patient was prescribed oral methylprednisolone at 40 mg once daily, with a tapering schedule: reduce by 4 mg weekly until reaching 20 mg/day, then reduce by 4 mg every two weeks. Maintenance therapy included monthly intramuscular hydroxycobalamin (100 µg).

Outcome and follow-up

At an outpatient follow-up on May 21, 2024 (8 months after discharge), the patient was on a maintenance dose of methylprednisolone 4 mg/day. Appetite, energy, sleep, and limb spasms had markedly improved. Follow-up laboratory tests showed a serum sodium level of 131 mmol/L and hemoglobin at 98 g/L. Despite ongoing monthly intramuscular hydroxocobalamin and oral iron supplementation, the hemoglobin level remained at 98 g/L, indicating persistent mild anemia. This incomplete recovery is consistent with the underlying autoimmune gastritis, which impairs both vitamin B12 and iron absorption. Continued monitoring and consideration of intravenous iron supplementation may be warranted if anemia does not further improve.

Discussion

This case illustrates a diagnostic journey that began with refractory hyponatremia and culminated in the identification of a multisystem autoimmune disorder. The patient was a 77-year-old male who presented with a two-month history of poor appetite, fatigue, and drowsiness. Severe hyponatremia (as low as 109 mmol/L) was consistently documented both at an outside hospital and our institution. The poor response to conventional sodium supplementation pointed towards an underlying, persistent sodium loss or a complex electrolyte disturbance.

The hyponatremia in this case stemmed from two interacting mechanisms, with central adrenal insufficiency as the predominant driver. This is evidenced by the classic biochemical profile (low morning cortisol with inappropriately low ACTH), elevated urinary sodium excretion indicating renal salt-wasting due to cortisol deficiency, and the rapid correction of serum sodium upon glucocorticoid replacement. Although overt cortisol deficiency precluded a formal diagnosis of SIADH, the well-established association between anti-LGI1 encephalitis and hyponatremia (reported in ~ 60% of cases) suggests that antibody-mediated ADH dysregulation likely played a secondary, exacerbating role. Thus, the refractory nature of the hyponatremia likely reflects the additive effect of predominant adrenal insufficiency and concurrent LGI1-related hypothalamic involvement. The temporal dissociation between symptom improvement and sodium correction provides strong evidence for dual contributors to the patient’s encephalopathy. While the global symptoms (drowsiness, fatigue) partially improved with sodium correction—consistent with a metabolic encephalopathy secondary to severe hyponatremia—the persistence of focal limb spasms, followed by their dramatic resolution solely with immunotherapy, strongly suggests that these specific deficits were primarily driven by the autoimmune inflammatory process. This pattern is highly characteristic of anti-LGI1 encephalitis, in which faciobrachial dystonic seizures are known to be immunotherapy-responsive and often occur independently of electrolyte disturbances. This interpretation is further corroborated by the bilateral hippocampal abnormalities on MRI and the detection of anti-LGI1 antibodies in the CSF.

The patient’s left limb spasms—detailed in Table 1—were clinically consistent with FBDS-like episodes in the setting of anti-LGI1 encephalitis, despite the absence of facial involvement. Although lower limb involvement is less typical in classical FBDS, the stereotyped, brief, high-frequency nature of these episodes, occurring without impaired awareness, is highly suggestive of this diagnosis. The lack of ictal EEG correlates further supports this interpretation. Critically, these focal spasms persisted despite the correction of serum sodium from 109 mmol/L to 117 mmol/L during initial treatment.

Central adrenal insufficiency is most often secondary to organic or functional disorders affecting the hypothalamic-pituitary region [3]. The patient concurrently exhibited multi-system clinical manifestations. Regarding the digestive system, symptoms included poor appetite (anorexia) and fatigue. Hematologically, macrocytic anemia (Hb 88 g/L, MCV 118 fL) was present, accompanied by deficiencies in vitamin B12 and iron. Neurologically, symptoms included drowsiness and left-sided limb spasms. This pattern of multi-system involvement suggested an underlying systemic disease. A definitive diagnosis of AIG was established via gastroscopy and subsequent pathological examination, which explained the patient’s anemia and some gastrointestinal symptoms. However, while hyponatremia can commonly cause generalized, non-specific muscle twitching [4], the focal nature of the spasms localized to the left limbs in this case was more specific, providing a preliminary indication of a distinct neurological focus. Furthermore, and critically, even after adequate replenishment of vitamin B12 and iron, along with aggressive correction of the hyponatremia, the patient’s neurological symptoms and refractory hyponatremia persisted. The persistence of anemia despite vitamin B12 and iron supplementation warrants further explanation. In autoimmune gastritis, autoantibodies target gastric parietal cells, leading to destruction of these cells and consequent loss of intrinsic factor production. Intrinsic factor is essential for the absorption of dietary vitamin B12 in the terminal ileum. Therefore, oral B12 replacement is ineffective in patients with AIG, and parenteral administration is required. Additionally, gastric achlorhydria impairs the reduction and absorption of non-heme iron, contributing to iron deficiency. In this patient, despite monthly intramuscular hydroxocobalamin and oral iron therapy, mild anemia persisted at the 8-month follow-up (hemoglobin 98 g/L), likely due to ongoing iron malabsorption or residual B12 deficiency. Intravenous iron supplementation may be considered if anemia does not improve further. This incomplete hematological recovery underscores the chronic nature of AIG and the need for long-term monitoring.

Given the persistence of the patient’s neurological symptoms and the refractory hyponatremia, coupled with the pre-existing diagnoses of psoriasis and AIG—both autoimmune in nature—the possibility of AE was considered. AE constitutes a group of disorders mediated by antibodies targeting antigens within the central nervous system. Based on the location of the target antigen, AE can be classified into two main categories: antibody-associated encephalitis targeting cell surface antigens, and that targeting intracellular antigens [5].Among these, anti-LGI1 antibody encephalitis is a common type of limbic encephalitis falling under the category of anti-cell surface antigen antibody-mediated disease [6]. LGI1 is a secreted protein involved in the regulation of synaptic signaling. Antibodies against LGI1 can disrupt normal neuronal function, leading to a characteristic clinical triad that includes limbic symptoms, faciobrachial dystonic seizures (FBDS), and hyponatremia [7]. LGI1 is primarily expressed in limbic system structures such as the hippocampus and amygdala. It functions by binding to presynaptic ADAM23 and postsynaptic ADAM22, forming a trans-synaptic complex that contributes to the regulation of voltage-gated potassium channel function and synaptic transmission [8, 9]. Anti-LGI1 antibodies are believed to interfere with this signaling pathway, leading to aberrant neuronal excitability and consequently generating the characteristic clinical manifestations.

In this case, the diagnosis of anti-LGI1 antibody-associated encephalitis is well-supported by multiple lines of evidence. The patient exhibited classic symptoms of limbic system involvement, including cognitive dysfunction (drowsiness and altered mental status) and seizure-like episodes (limb spasms). Brain MRI revealed bilateral hippocampal T2-FLAIR hyperintensity and swelling, findings that are characteristic of limbic encephalitis. The definitive confirmation was provided by the positive anti-LGI1 antibody in the cerebrospinal fluid (titer 1:64).Furthermore, the patient’s associated refractory hyponatremia is a prominent feature of this specific encephalitis subtype. Approximately 60% of patients with anti-LGI1 encephalitis develop hyponatremia [10]. The underlying mechanism is thought to involve antibody-mediated interference with hypothalamic function, potentially disrupting the regulation of antidiuretic hormone.

The clustering of psoriasis, AIG, and anti-LGI1 encephalitis in this patient is noteworthy. Literature review indicates that psoriasis is associated with various autoimmune conditions, including inflammatory bowel disease, rheumatoid arthritis, and autoimmune thyroid disease; however, its overlap with AIG and neurological autoimmune disorders is rarely reported. Regarding genetic susceptibility, psoriasis is known to be strongly associated with the HLA-Cw6 allele [11], while AIG has established links with polymorphisms in the HLA-DR/DQ region (e.g., DRB1*04, DQB1*03) [12]. Notably, anti-LGI1 encephalitis has also been shown to have a significant association with specific HLA subtypes, particularly DRB1*07:01 and DQB1*02:02 [13], suggesting a potential shared genetic background. The coexistence or linkage disequilibrium of these HLA alleles may have provided the genetic basis for multi-organ autoimmunity in this patient. Although complete overlap of all three conditions has not been previously reported in the literature, “autoimmune clustering” in a single patient is not uncommon, reminding clinicians that the identification of one organ-specific autoimmune disease should prompt vigilance for involvement of other systems.We hypothesize that the rare co-occurrence of psoriasis, AIG and anti-LGI1 encephalitis in this patient may be linked through shared immunopathogenic pathways, potentially centered on the Th17/IL-23/IL-17 axis. The core pathogenesis of psoriasis involves the overactivation of Th17 cells and dysregulation of this specific inflammatory pathway [14]. It is plausible that systemic immune dysregulation, possibly involving cytokines such as IL-17, could influence the central nervous system and gastric mucosa, although direct evidence for such mechanisms in anti-LGI1 encephalitis or AIG is currently lacking. The detection of a positive anti-Jo-1 antibody and a high-titer antinuclear antibody (1:320) further supports the presence of broad systemic autoimmune dysregulation in this patient. This immunological background, potentially influenced by a Th17-skewed milieu, may have predisposed multiple organs to autoimmune attack. Furthermore, an accumulation of genetic susceptibility is likely, where alleles conferring risk for psoriasis (e.g., HLA-Cw6) and those associated with AIG (e.g., in the HLA-DR/DQ region) may have co-existed in this patient, significantly amplifying the risk for multi-organ autoimmune reactions [15]. The coexistence of anti-LGI1 antibodies and anti-parietal cell antibodies strongly implies widespread B-cell activation and the phenomenon of “epitope spreading,” wherein an initial immune response against one organ (e.g., skin or stomach) expands over time to target structurally or immunologically linked antigens within the central nervous system, such as LGI1 [16], culminating in multi-system immune attack. The favorable response to glucocorticoid therapy across all three conditions supports the presence of a shared reversible inflammatory component, but the precise immunological pathways involved require further investigation.

This case highlights the rare co-occurrence of psoriasis, AIG and anti-LGI1 encephalitis presenting with refractory hyponatremia due to pituitary involvement and central adrenal insufficiency, a systemic Th17/IL-23/IL-17 immunophenotype that has not been sufficiently emphasized in the literature. It therefore underscores that in patients with refractory hyponatremia accompanied by multisystem manifestations and poor response to conventional therapy, clinicians should maintain a broad diagnostic perspective and suspect multi-organ autoimmune involvement. Identifying one autoimmune condition should prompt a systematic evaluation for concomitant immune-mediated disease across other organ systems, which is essential for accurate diagnosis and effective management.

Abbreviations

14C-UBT

14C-urea breath test\

ACTH

Adrenocorticotropic hormone

ADAM

A disintegrin and metalloprotease

ADH

Antidiuretic hormone

AE

Autoimmune encephalitis

AIG

Autoimmune gastritis

ANA

Antinuclear antibody

BMI

Body mass index

CASPR2

Contactin-associated protein-like 2

CMV

Cytomegalovirus

CSF

Cerebrospinal fluid

CT

Computed tomography

EBV

Epstein-Barr virus

EEG

Electroencephalography

FBDS

Faciobrachial dystonic seizures

FLAIR

Fluid-attenuated inversion recovery

FSH

Follicle-stimulating hormone

FT3

Free triiodothyronine

FT4

Free thyroxine

GABABR

Gamma-aminobutyric acid B receptor

Hb

Hemoglobin

HE

Hematoxylin and eosin

HLA

Human leukocyte antigen

HP

Helicobacter pylori

Ig

Immunoglobulin

IL

Interleukin

ISO

International Organization for Standardization

Jo-1

Anti-Jo-1 antibody (histidyl-tRNA synthetase)

LGI1

Leucine-rich glioma-inactivated 1

LH

Luteinizing hormone

MCV

Mean corpuscular volume

MMSE

Mini-Mental State Examination

MoCA

Montreal Cognitive Assessment

MRI

Magnetic resonance imaging

NE%

Neutrophil percentage

NMDAR

N-methyl-D-aspartate receptor

PCR

Polymerase chain reaction

PG I

Pepsinogen I

PG II

Pepsinogen II

PLT

Platelet

PPD

Purified protein derivative (tuberculin skin test)

PRL

Prolactin

SIADH

Syndrome of inappropriate antidiuretic hormone secretion

T-SPOT.TB

T-SPOT tuberculosis test

Th17

T helper 17 cells

TSH

Thyroid-stimulating hormone

WBC

White blood cell

Authors’ contributions

Wenyan Sun : Literature review, collation of laboratory and imaging data, statistical analysis of clinical indicators, and assistance in drafting the initial manuscript. Additionally, responsible for all manuscript revision work during the peer-review stage, and finalization of the revised draft for resubmission.Cunkai Wang : Conceptualization of the study, clinical data collection (including patient history and follow-up records), drafting the initial manuscript, and revising the clinical discussion section.Yumeng Wang : Participation in the diagnostic reasoning process, verification of laboratory test results, and revision of the “Investigations” section of the manuscript.Hongyu Liu : Collection of gastroscopic findings and pathological data, preparation of imaging figures (Figs. 2, 3, 4 and 5), and proofreading of clinical procedure descriptions.Jian Zhang : Assistance in clinical treatment plan formulation, recording of therapeutic responses, and supplementation of the “Treatment” section details.Yun Bai : Supervision of the entire study design, final diagnosis confirmation, manuscript revision and finalization, and correspondence with the journal. Responsible for ensuring the accuracy and integrity of all data.All authors have read and approved the final manuscript, and confirm that the contributions are accurately described without omissions or misattributions.

Funding

Recipient: Yun Bai.

Grant ID: ZF2026001.

Funding Source: Excellent Talents Program in Clinical Medicine, Supported by Hebei Provincial Government.

Data availability

All data generated or analyzed during this study are included in this published article. The datasets used and/or analyzed during the current study are available from the author on reasonable request.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Written informed consent for publication of this case report and any accompanying images was obtained from the patient. A copy of the written consent is available for review by the Editor of BMC Neurology upon request.

Competing interests

The authors declare no competing interests.