Relation between peripheral blood inflammatory indices and severity of central retinal artery occlusion.

Background: Central retinal artery occlusion (CRAO) has been identified as an acute emergency resulting in vision loss, with its pathogenesis potentially involving systemic inflammation and abnormal lipid metabolism. Over recent years, it has been established that peripheral blood inflammatory indices, including the neutrophil-to-lymphocyte ratio (NLR), the systemic immunoinflammatory index (SII), and the monocyte-to-high-density lipoprotein ratio (MHR), play significant roles in assessing systemic inflammation and lipid metabolism. However, the role of these indices in assessing the severity of CRAO has rarely been explored. This study aimd to investigate the relationship between these inflammatory indices and the severity of CRAO. Methods: This was a retrospective clinical study with a total of 49 CRAO patients and 50 age- and sex-matched controls involved. The patients with CRAO were divided into three groups (13 with incomplete CRAO, 16 with subtotal CRAO and 20 with total CRAO). Data were compared across these groups, and additionally, correlation analysis, restricted cubic spline plots, and receiver operating characteristic curve analysis were performed. Results: The values of NLR, SII and MHR were significantly higher in the CRAO group compared to controls (NLR: 2.49(1.71,3.44) vs 1.60(1.24,1.97), P<0.001; SII: 606.46(410.25,864.35) vs 403.91(332.90,524.31), P=0.001; MHR: 0.33(0.26,0.44) vs 0.25(0.21,0.34), P<0.001). MHR was also significantly higher in total CRAO than in incomplete CRAO and subtotal CRAO (0.41(0.32,0.60) vs 0.29(0.21,0.43), P=0.036; 0.41(0.32,0.60) vs 0.29(0.23,0.38), P=0.017). Significant positive associations were found between MHR, NLR, SII and both the incidence (all P<0.001) and severity (P<0.001, P<0.001, P=0.003, respectively) of CRAO. MHR had a linear relationship with both the occurrence and severity of CRAO (P-overall=0.013, P-non-linear=0.427 and P-overall=0.013, P-non-linear=0.825). Combining MHR and NLR significantly improved diagnostic efficacy for CRAO and total CRAO, with area under the curve of 0.816 and 0.827, respectively, compared to using MHR alone (0.705 and 0.816). Conclusion: Elevated levels of peripheral blood NLR, SII, and MHR are positively associated with CRAO incidence, highlighting their potential as early predictive markers. The combined NLR and MHR index further enhances diagnostic accuracy and may facilitate timely assessment of CRAO severity by ophthalmologists and internists.

Plasma Proteomics to Identify Drug Targets and Potential Drugs for Retinal Artery Occlusion: An Integrated Analysis in the UK Biobank.

Retinal artery occlusion (RAO), which is positively correlated with acute ischemic stroke (IS) and results in severe visual impairment, lacks effective intervention drugs. This study aims to perform integrated analysis using UK Biobank plasma proteome data of RAO and IS to identify potential targets and preventive drugs. A total of 7191 participants (22 RAO patients, 1457 IS patients, 8 individuals with both RAO and IS, and 5704 healthy age-gender-matched controls) were included in this study. Unique 1461 protein expression profiles of RAO, IS, and the combined data set, extracted from UK Biobank Plasma proteomics projects, were analyzed using both differential expression analysis and elastic network regression (Enet) methods to identify shared key proteins. Subsequent analyses, including single cell type expression assessment, pathway enrichment, and druggability analysis, were conducted for verifying shared key proteins and discovery of new drugs. Five proteins were found to be shared among the samples, with all of them showing upregulation. Notably, adhesion G-protein coupled receptor G1 (ADGRG1) exhibited high expression in glial cells of the brain and eye tissues. Gene set enrichment analysis revealed pathways associated with lipid metabolism and vascular regulation and inflammation. Druggability analysis unveiled 15 drug candidates targeting ADGRG1, which demonstrated protective effects against RAO, especially troglitazone (-8.5 kcal/mol). Our study identified novel risk proteins and therapeutic drugs associated with the rare disease RAO, providing valuable insights into potential intervention strategies.

Circulating serum fibroblast growth factor 21 as risk and prognostic biomarker of retinal artery occlusion.

To evaluate the predictive and prognostic value of fibroblast growth factor 21 (FGF21) levels in retinal artery occlusion (RAO) patients. In this case-control study, serum FGF21 levels were detected by using the ELISA method. Multivariable logistic regression analyses were performed to evaluate the significance of FGF21 in assessing the risk of developing RAO and its impact on vision and concurrent ischemic stroke. Compared with control group, serum FGF21 levels were significantly higher (median [IQR] = 230.90[167.40,332.20] pg/ml) in RAO patients. Multivariate logistic regression analysis showed that elevated serum FGF21 levels were associated with a higher risk of RAO occurrence (P = 0.025, OR [95%CI] = 9.672 [2.573, 36.359]) after adjustment for multiple confounding factors. Higher serum FGF21 levels were negatively associated with visual acuity improvement (P = 0.029, OR [95%CI] = 0.466[0.235, 0.925]) and positively correlated with concurrent ischemic stroke (P = 0.04, OR [95% CI] = 1.944[1.029, 3.672]) in RAO patients. Elevated serum FGF21 levels could promote the development of RAO and indicate worse visual prognosis and increase the risk of concurrent ischemic stroke, which might help clinicians early diagnose and treat RAO patients.

Plasmalogens and Octanoylcarnitine Serve as Early Warnings for Central Retinal Artery Occlusion.

Central retinal artery occlusion (CRAO) is a kind of ophthalmic emergency which may cause loss of functional visual acuity. However, the limited treatment options emphasize the significance of early disease prevention. Metabolomics has the potential to be a powerful tool for early identification of individuals at risk of CRAO. The aim of the study was to identify potential biomarkers for CRAO through a comprehensive analysis. We employed metabolomics analysis to compare venous blood samples from CRAO patients with cataract patients for the venous difference, as well as arterial and venous blood from CRAO patients for the arteriovenous difference. The analysis of metabolites showed that PC(P-18:0/22:6(4Z,7Z,10Z,13Z,16Z,19Z)), PC(P-18:0/20:4(5Z,8Z,11Z,14Z)) and octanoylcarnitine were strongly correlated with CRAO. We also used univariate logistic regression, random forest (RF), and support vector machine (SVM) to screen clinical parameters of patients and found that HDL-C and ApoA1 showed significant predictive efficacy in CRAO patients. We compared the predictive performance of the clinical parameter model with combined model. The prediction efficiency of the combined model was significantly better with area under the receiver operating characteristic curve (AUROC) of 0.815. Decision curve analysis (DCA) also exhibited a notably higher net benefit rate. These results underscored the potency of these three substances as robust predictors of CRAO occurrence.

Central Retinal Artery Occlusion in Rhino-Orbital-Cerebral Mucormycosis: An Inflammatory-Prothrombotic State.

PURPOSE: The aim was to evaluate patient profiles of rhino-orbital-cerebral mucormycosis (ROCM) cases with central retinal artery occlusion (CRAO) postcoronavirus disease 2019. DESIGN: A nonrandomized retrospective case-control study. METHODS: The ROCM cases presenting with CRAO were compared with a control ROCM group without CRAO at a tertiary care center. Demography, systemic status, clinical features, histopathology, imaging, and blood profile were assessed for any specific risk factors. RESULTS: A total of 12 patients were seen in the CRAO group and 16 in the non-CRAO group. The male-to-female ratio was 3:1 with a mean age of 49.5 years. In the CRAO group, 75% had diabetes mellitus with mean hemoglobin A1c of 9.03%, and 66.7% had received steroid treatment. All cases were histopathologically confirmed positive for mucor. There was a significant difference in mean D-dimer and serum ferritin between the 2 groups, with higher level in the CRAO group. All patients with CRAO had light perception-negative vision, with total ophthalmoplegia and proptosis seen in 66.7% of cases. Four patients had orbital apex involvement, 5 had cavernous sinus involvement, and 8 had intracranial involvement in the CRAO group. CONCLUSIONS: Inflammatory markers D-dimer and serum ferritin were significantly associated with CRAO, suggestive of hyperinflammatory and hypercoagulable state. A high index of suspicion should be maintained in cases with elevated markers and prophylactic anticoagulants can be started to prevent CRAO in a subset of patients.

Serum sortilin as a predictor of stroke in patients with intermediate carotid artery stenosis.

BACKGROUND: Sortilin was an important molecular protein involved in the pathogenesis of atherosclerosis. Besides, serum sortilin was associated with adverse cerebrovascular events. Atherosclerotic stenosis in the carotid artery is a major etiology for ischemic stroke. The risk of stroke in patients with intermediate carotid artery stenosis (CAS) was unknown. Hence, the aim of the present study was to evaluate the relationship between serum sortilin levels and stroke in patients with intermediate CAS. METHODS: A total of 195 intermediate CAS patients were included in this cross-sectional study. The patients were divided into two groups as symptomatic (N = 95) and asymptomatic (N = 100) patients. Patients with a transient ischemic attack (TIA), retinal ischemic event, or ischemic stroke resulting from the narrowed carotid artery were considered to be symptomatic. Serum sortilin concentrations were measured using the enzyme-linked immunosorbent assay. RESULTS: Serum sortilin level was significantly higher in the symptomatic group than in the severe asymptomatic group (1.53 ± 0.25 ng/mL vs 1.34 ± 0.19 ng/mL, p < 0.001). Besides, high serum sortilin levels (odds ratio = 4.91, 95% confidence intervals 1.24-19.51, p = 0.023) were identified as independent predictors of symptomatic carotid plaque. In the receiver operating characteristic curve analysis, serum sortilin levels higher than 1.34 ng/mL predicted stroke/TIA with a sensitivity of 66.3% and a specificity of 67% (AUC = 0.725, p < 0.001). CONCLUSIONS: Serum sortilin level is increased in the presence of symptomatic intermediate CAS and may have clinical value in the management of patients with carotid artery disease.

Neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) are more prominent in retinal artery occlusion (RAO) compared to retinal vein occlusion (RVO).

AIM: To evaluate the association between the value of neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), monocyte to high-density lipoprotein ratio (MHR) and the development of retinal artery occlusion (RAO) and retinal vein occlusion (RVO). METHODS: This retrospective study assessed 41 RAO, 50 RVO and 50 control (age and gender matched senile cataract) participants. The NLR, PLR and MHR parameters of patients' peripheral blood were analyzed. A receiver operating characteristics (ROC) curve analysis and the best cutoff value were used to specify the predictive value of NLR, PLR and MHR in RAO and RVO. RESULTS: The NLR, PLR and MHR were significantly higher in RAO group compared to the control group (p<0.001, p<0.001 and p = 0.008; respectively). The NLR, PLR and MHR were also significantly higher in the RVO group compared to the control group (p<0.001, p = 0.001 and p = 0.012, respectively). The NLR and PLR were significantly higher in the RAO group compared to the RVO group (p<0.001 and p = 0.022, respectively). The optimal cut-off value of NLR to predict RAO was >2.99, with 90.2% sensitivity and 100% specificity. The PLR to predict RAO was > 145.52, with 75.6% sensitivity and 80.0% specificity. CONCLUSION: Higher NLR, PLR and MHR are related to the occurrence of RAO and RVO. NLR and PLR are more prominent in RAO compared to RVO.

Complete blood cell count measures in retinal artey occlusions.

PURPOSE: To investigate the role of complete blood cell count (CBC) measures in retinal artery occlusion (RAO). METHODS: This was a case-control study, including 73 newly diagnosed RAO patients and 73 sex- and age-matched subjects without RAO. On the same day of RAO diagnosis, a blood sample was collected and CBC was determined using an automatic blood counter. Dimensional CBC indices, such as mean platelet volume (MPV) and red cell distribution width (RDW), and some CBC-combined indices, including neutrophil/lymphocyte ratio (NLR), derived NLR [dNLR = neutrophils/(white blood cells - neutrophils)] and platelet/lymphocyte ratio (PLR), were evaluated. Erythrocyte sedimentation rate (ESR) was also measured. RESULTS: Median neutrophils, red cell distribution width (RDW), NLR and dNLR were 4.5x109 /L (IQR = 3.8-5.8), 13.4% (IQR = 12.7-14.75), 2.47 (IQR = 1.85-3.13) and 1.70 (IQR = 1.26-2.18) in RAO patients and 4x109 /L (IQR = 3.18-4.93), 12.9% (IQR = 12-14), 1.86 (IQR = 1.42-2.44) and 1.32 (IQR = 1.02-1.64) in controls. RAO patients had significantly higher values of neutrophils (p = 0.003), RDW (p = 0.0011), NLR (p = 0.0001) and dNLR (p = 0.0001). There were no significant differences between the values of white blood cells, lymphocytes, platelet count, MPV and PLR. Multivariate logistic regression models revealed a statistically significant correlation between RAO and increased RDW (OR = 1.36, 95% CI = 1.06-1.73, p = 0.015), NLR (OR = 2.02, 95% CI = 1.34-3.06, p = 0.0009) and dNLR (OR = 3.4, 95% CI = 1.71-6.75, p = 0.0005). CONCLUSION: Results suggest that RDW, NLR and dNLR may be involved in the pathogenesis of RAO and predict its occurrence. However, high-quality epidemiologic studies, preferably of cohort design, are warranted to confirm whether, or not, an RDW, NLR and dNLR may be considered potential biomarkers of RAO.

Neutrophil to Lymphocyte Ratio (NLR) is a Better Tool Rather than Monocyte to High-Density Lipoprotein Ratio (MHR) and Platelet to Lymphocyte Ratio (PLR) in Central Retinal Artery Occlusions.

Purpose: To evaluate the predictive value of neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), monocyte to high-density lipoprotein (HDL) ratio (MHR) and blood lipid profile in central retinal artery occlusion (CRAO) patients.Methods: We included 37 patients with a diagnosis of CRAO and 36 healthy subjects with similar age-sex in the study. We analyzed the medical records of peripheral blood samples retrospectively. NLR, PLR, MHR were obtained by simple manually calculations.Results: CRAO patients had significantly higher mean NLR in comparison with healthy subjects (p: 0.009). The groups were similar in regard to mean PLR (p: 0.864) and mean MHR (p: 0.581). A cutoff value of >1.62 for NLR was found to be a diagnostic tool in CRAO. The sensitivity and specificity for this cutoff point was 83.8% and 55.6%, respectively.Conclusion: NLR rather than MHR and PLR may be a beneficial marker for the development of CRAO.

Carotid artery intima-media thickness, HDL cholesterol levels, and gender associated with poor visual acuity in patients with branch retinal artery occlusion.

PURPOSE: To investigate factors associated with poor visual acuity (VA) in branch retinal artery occlusion (BRAO). METHODS: This was a retrospective cross-sectional study of 72 eyes with BRAO of 72 patients. For statistical comparison, we divided the patients into worse-VA (decimal VA < 0.5) and better-VA (decimal VA > = 0.5) groups. We examined the association of clinical findings, including blood biochemical test data and carotid artery ultrasound parameters, with poor VA. RESULTS: Median age, hematocrit, hemoglobin and high-density lipoprotein (HDL) differed significantly between the groups (P = 0.018, P < 0.01, P < 0.01, and P = 0.025). There was a tendency towards higher median IMT-Bmax in the worse-VA group (worse-VA vs. better-VA: 2.70 mm vs. 1.60 mm, P = 0.152). Spearman's rank correlation test revealed that logMAR VA was significantly correlated to IMT-Bmax (rs = 0.31, P < 0.01) and IMT-Cmax (rs = 0.24, P = 0.035). Furthermore, logMAR VA was significantly correlated to HDL level (rs = -0.33, P < 0.01). Multivariate logistic regression analysis revealed that IMT-Bmax (odds ratio [OR] = 2.70, P = 0.049), HDL level (OR = 0.91, P = 0.032), and female gender (OR = 15.63, P = 0.032) were independently associated with worse VA in BRAO. CONCLUSIONS: We found that increased IMT-Bmax, decreased HDL, and female sex were associated with poor VA in BRAO patients. Our findings might suggest novel risk factors for visual dysfunction in BRAO and may provide new insights into the pathomechanisms underlying BRAO.

Non-Occlusive Retinal Vascular Inflammation and Role of Red Blood Cell Deformability in Birdshot Chorioretinopathy.

Purpose: To investigate differences in red blood cell (RBC) deformability between birdshot chorioretinopathy (BCR) subjects and matched controls, and to postulate its relationship with lack of vascular occlusion in BCR. Methods: In a single center, prospective, non-randomized mechanistic study, blood samples were collected from eight healthy controls and nine BCR patients, and subjected to biochemical and hematological tests, as well as RBC indices assessment using dual-beam optical tweezers. Results: The mean age of the controls was 52.37 ± 10.70 years and BCR patients was 53.44 ± 12.39 years. Initial cell size (Io) for the controls was 8.48 ± 0.25 µm and 8.87 ± 0.31 µm for BCR RBCs (p = 0.014). The deformability index (DI) for the controls was 0.066 ± 0.02 and that for BCR RBCs was 0.063 ± 0.03 (p = 0.441). Conclusion: There was no statistically significant difference in DI between RBCs from BCR and healthy controls. This may explain the rare occurrence of retinal vascular occlusion despite the underlying vasculitic pathophysiology of BCR.

A case report of branch retinal artery occlusion in a teenager due to hyperhomocysteinaemia; the interplay of genetic and nutritional defects.

BACKGROUND: Retinal vascular occlusions are uncommon in young people and require more in-depth investigation into the cause. Studies have revealed that a high level of circulating homocysteine poses a risk for retinal vaso-occlusive events across a wide age range. This case report reflects on how the interplay of genetic mutation and vitamin deficiency can cause a pathological level of homocysteine with resultant branch retinal artery occlusion in a young patient. CASE PRESENTATION: A 16-year-old boy presented to eye casualty with acute inferior visual field loss in the left eye. Visual acuity remained normal at 6/6 each eye and the event was painless. Initial assessment, and retinal photography revealed a left superior hemi-field branch retinal artery occlusion with macular sparing. Given the patient's age, extensive investigation into the cause was carried out. Positive findings were of an elevated level of homocysteine as a result of vitamin B12 and folic acid deficiency as well as a genetic mutation in the MTHFR gene (encoding MTHFR enzyme which is vital in normal homocysteine metabolism). Vitamin B12 and folic acid were replaced which in turn normalized the patient's homocysteine levels. At two months, the patient's visual fields had also improved, and no further vascular event had occurred. CONCLUSIONS: This case report has highlighted the link between hyperhomocysteinaemia and retinal artery occlusion. However, despite vitamin replacement being shown to normalize homocysteine levels, no evidence exists to date as to whether this will reduce the risk of further retinal vascular occlusion.

Homocysteine in retinal artery occlusive disease: A meta-analysis of cohort studies.

Few studies have reported the relationship between retinal artery occlusion (RAO) and plasma homocysteine (Hcy) levels. Our goal was to evaluate the association between the plasma Hcy level and the risk of RAO disease. Several databases were searched for all published studies that involved Hcy and RAO. Six studies evaluated hyperhomocysteinemia (hHcy) in retinal artery occlusion patients and controls; the incidence of hHcy in patients with RAO was higher than the control and the pooled odds ratio (OR) was 6.64 (95% confidence interval (CI): 3.42, 12.89). Subgroup analyses showed that the ORs were 4.77 (95% CI: 2.69, 8.46) in Western countries, 22.19 (95% CI: 2.46, 200.37) in Asian countries, 9.70 (95% CI: 4.43, 21.20) in the age matched group, 11.41 (95% CI: 3.32, 39.18) in the sex matched group, 9.70 (95% CI: 4.37, 21.53) in the healthy control group, and 6.82 (95% CI: 4.19, 11.10) in the sample size >30. The mean plasma Hcy level from 5 case-control studies was higher than controls, and the weighted mean difference (WMD) was 6.54 (95% CI: 2.79, 10.29). Retinal artery occlusion is associated with elevated plasma Hcy levels. Our study results suggest that hHcy is probably an independent risk factor for RAO.

Mean platelet volume in patients with retinal artery occlusion.

PURPOSE: The aim of this study was to investigate the mean platelet volume (MPV) of patients with retinal artery occlusion (RAO). METHODS: Thirty-seven patients diagnosed with RAO and 32 control subjects were included in this retrospective study. Retinal artery occlusion was diagnosed on the basis of clinical examination and fundus fluorescein angiography. All participants underwent complete ocular examination, and MPV, hematocrit, hemoglobin, and platelet counts were recorded. RAO patient data were compared with those of the control subjects. RESULTS: Patients with RAO had significantly higher MPV values (7.96 ± 1.2 fL) compared with control subjects (7.33 ± 0.7 fL, p<0.001). No significant difference was found with regard to platelet count between the RAO group and the control group (262 ± 70.1 × 109/L and 251 ± 56.6 × 109/L, respectively, p=0.50). MPV was an independent predictor of RAO [odds ratio (OR)=0.50; 95% confidence interval (CI)=0.28-0.89; p=0.019). CONCLUSIONS: Our results demonstrated that MPV values were significantly higher in patients with RAO, suggesting that larger platelets may contribute to the pathogenesis of the RAOs.

Mean platelet volume in patients with retinal artery occlusion / Volume médio de plaquetas em pacientes com oclusão da artéria da retina

ABSTRACT Purpose: The aim of this study was to investigate the mean platelet volume (MPV) of patients with retinal artery occlusion (RAO). Methods: Thirty-seven patients diagnosed with RAO and 32 control subjects were included in this retrospective study. Retinal artery occlusion was diagnosed on the basis of clinical examination and fundus fluorescein angiography. All participants underwent complete ocular examination, and MPV, hematocrit, hemoglobin, and platelet counts were recorded. RAO patient data were compared with those of the control subjects. Results: Patients with RAO had significantly higher MPV values (7.96 ± 1.2 fL) compared with control subjects (7.33 ± 0.7 fL, p<0.001). No significant difference was found with regard to platelet count between the RAO group and the control group (262 ± 70.1 × 109/L and 251 ± 56.6 × 109/L, respectively, p=0.50). MPV was an independent predictor of RAO [odds ratio (OR)=0.50; 95% confidence interval (CI)=0.28-0.89; p=0.019). Conclusions: Our results demonstrated that MPV values were significantly higher in patients with RAO, suggesting that larger platelets may contribute to the pathogenesis of the RAOs.

RESUMO Objetivo: O objetivo deste estudo foi investigar o volume plaquetário médio (MPV) de pacientes com oclusão da artéria da retina (RAO). Métodos: Trinta e sete pacientes com diagnóstico de RAO e 32 indivíduos do grupo controle foram incluídos neste estudo retrospectivo. A oclusão da artéria da retina foi diagnosticada com base em exame clínico e angiofluoresceinografia. Todos os participantes foram submetidos ao exame ocular completo. MPV, hematócrito, hemoglobina e contagem de plaquetas dos participantes foram registrados. Os dados dos pacientes com RAO foi comparado com os de sujeitos do grupo controle. Resultados: Pacientes com RAO apresentaram valores significativamente mais elevados MPV (7,96 ± 1,2 fL) em comparação aos indivíduos do grupo controle (7,33 ± 0,7 fL) (p<0,001). Nenhuma diferença significativa foi encontrada no número de plaquetas entre os grupos RAO e controle (262 ± 70,1 109/L and 251 ± 56,6 109/L, respectivamente, p=0,50). MPV foi um preditor independente de RAO (odds ratio (OR)=0,50; intervalo de confiança de 95% (IC)=0,28-0,89; p=0,019). Conclusões: Os resultados demonstraram que os valores de MPV foram significativamente maiores nos pacientes com RAO, sugerindo que plaquetas maiores podem contribuir na patogênese da RAO.

Central retinal artery occlusion in a 13-year-old child as a presenting sign of hyperhomocysteinemia together with high lipoprotein(a) level.

BACKGROUND: We describe a child with central retinal artery occlusion and hyperhomocysteinemia. METHODS: A 13-year-old girl developed sudden vision loss and was hospitalized for diagnosis and treatment. RESULTS: Her physical examination was normal except for her ophthalmologic examination. Her serum homocysteine level and lipoprotein(a) were elevated to 45.27 µmol/L and 61 mg/dL 0-29 mg/dL, respectively. A homozygous mutation was identified for methylenetetrahydrofolate reductase at position C677T. CONCLUSION: This report documents central retinal artery occlusion associated with the risk factors of hyperhomocysteinemia caused by methylenetetrahydrofolate reductase C677 T mutation and high lipoprotein(a) level in a child. Retinal artery occlusion is rare in children. This patient emphasizes the need for a systemic evaluation for hyperhomocysteinemia and lipoprotein(a) levels in children with retinal vascular occlusion of uncertain etiology.