Prevalence of autoimmunity in patients of chronic urticaria – A cross-sectional pilot study from Eastern India

INTRODUCTION

Chronic spontaneous urticaria (CSU) is a prevalent skin disorder marked by the daily or nearly daily occurrence of hives and/or angioedema for over 6 weeks.^[1] Despite its high prevalence, the pathogenesis of CSU remains complex and challenging to manage. CSU has recently been classified into two endotypes: autoallergic type (type 1), mediated by immunoglobulin E (IgE) antibodies, and autoimmune type (type 2b), mediated by immunoglobulin G antibodies.^[2] The prevalence and pathogenesis of these endotypes vary by geographic region, genetics, and environmental factors. Autoimmunity is increasingly recognized as a major causative factor, particularly in therapy-resistant cases. Autoimmune CSU is linked to autoantibodies against self-antigens such as thyroid peroxidase (TPO), nuclear antigens (ANA), and IgE receptors High Affinity IgE receptor (FcεRI), with their detection aiding in identifying endotypic variations and disease severity.^[3-5] However, diagnostic methods for autoimmune CSU are not standardized, and their availability and accuracy are limited. In India, where allergic disorders, including CSU, are widespread, data on the prevalence of CSU and endotypic variations are scarce, and the clinico-epidemiological profile remains largely unknown.^[6,7] Therefore, there is a critical need for further research to explore the epidemiology and potential endotypic diversity of CSU in this region.

We conducted a pilot study to assess the prevalence of autoimmunity in CSU patients at a tertiary healthcare institution in eastern India. Our goal was to explore the endotypic variation and clinico-epidemiological profile of CSU in this population. We hypothesized that autoimmunity is a significant etiological factor for CSU in our region and contributes to disease severity and impact.

MATERIAL AND METHODS

This study was a hospital-based observational cross-sectional design to investigate the prevalence of autoimmunity in patients with CSU in eastern India. The study was conducted at the dermatology outpatient department of a tertiary care hospital.

The study population consisted of 30 patients with CSU who attended the dermatology outpatient department during the 4-month study period. The inclusion criteria were patients aged 18 years and above, diagnosed with CSU (hives and/or angioedema for more than 6 weeks), and who gave informed written consent to participate in the study.

Data collection involved a detailed clinical examination and history taking. The disease activity was assessed using the Urticaria Activity Score 7 (UAS7), which is a validated tool for measuring the severity of CSU. The autologous serum skin test (ASST) was performed by taking 5 mL of venous blood and was left to coagulate for half an hour at room temperature in a sterile container. A 1 mL insulin syringe (30-gauge needle) was used to inject 0.05 mL of autologous serum intradermally into the left forearm, 2 cm below the cubital fossa, after the serum had been centrifuged for 15 min at 2000 revolutions per minute. Similarly, the right forearm received an intradermal injection of 0.05 mL of 0.9% sterile normal saline (negative control) proximally. Within 30 minutes, a serum-induced erythematous weal that was 1.5 mm in diameter larger than the saline-induced reaction was considered positive to help evaluate the presence of functional autoantibodies.^[8]

Blood samples were collected from all participants for laboratory investigations. These included complete blood count, erythrocyte sedimentation rate, C-reactive protein (CRP), serum IgE levels, and thyroid function tests. Enzyme-linked immunosorbent assay (ELISA) with commercial kits was performed to detect the presence of autoantibodies against TPO with an intraassay coefficient of variation of 5.7% and interassay coefficient of variation of 8.0% with cut off 55 IU/mL, nuclear antigens (ANA by Hep 2 cell line), and rheumatoid factor (RF factor) with slide agglutination method with agglutination indicating a RF concentration >8 IU/mL [Figure 1].

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Figure 1:

Flowchart depicting the methodology of the study. CBC: Complete blood count, ESR: Erythrocyte sedimentation rate, CRP: C reactive protein, IgE: Immunoglobulin E, ANA: antinuclear antibodies, RF: Rheumatoid Factor, ANti-TPO: Anti Thyroid peroxidase antibody.

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The data underwent analysis through descriptive statistics. The prevalence of autoimmunity was calculated as the proportion of patients with at least one positive autoantibody. The exploration of associations between autoimmunity and clinico-epidemiological variables involved the utilization of the Chi-square test or Fisher’s exact test for categorical variables and the t-test or Mann-Whitney U-test for continuous variables. A P < 0.05 was considered statistically significant.

The ethical clearance for this study was duly procured from the Institutional Ethics Committee. Every participant in the study presented written informed consent before their inclusion. The conduct of the study adhered to the tenets of the Declaration of Helsinki and Good Clinical Practice guidelines.

RESULTS

Table 1 shows the demographic profile of our study population. The mean age of patients was 30.6 ± 11.75 years, and the mean duration of urticaria was 18.46 ± 23.72 months. The average age of onset was 28.56 ± 11.47 years. There were more females (67%) than males (33%) in our study.

Table 2 shows the prevalence of autoimmunity in our study population. We found that 33.33% of our patients had at least one positive autoantibody, indicating autoimmune CSU. The most common autoantibody was anti-TPO (40%), followed by ANA (20%), RF (10%), and others (30%). Three patients in the “others” category were diagnosed with pre-existing conditions, including myasthenia gravis, pernicious anemia, and spondyloarthropathy, with autoantibodies present for each respective disease.

Of the 30 patients included, 10 (66.7%) patients had at least one autoimmune marker positive and were designated as type 1 CSU. Table 3 shows the association between autoimmunity and clinico-epidemiological variables. We found that autoimmune CSU was associated with higher levels of CRP and lower levels of serum IgE than autoallergic CSU.

We found that 25% of type 1 urticaria patients and 70% of type 2b urticaria patients had elevated CRP levels. This difference in association was statistically significant (P = 0.018) [Figure 2]. Our study also depicted that patients with angioedema had a more severe form of the disease and significantly higher UAS7 scores than those without angioedema (P = 0.007) [Figure 3].

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Figure 2:

Graph depicting elevated C-reactive protein (CRP) levels in autoimmune chronic spontaneous urticaria (CSU) in comparison to autoallergic CSU.

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Figure 3:

Box plot of urticaria activity score 7 in patients with or without angioedema. CRP: C-reactive protein.

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Type 1 autoallergic type of CSU had a significantly higher level of serum IgE in comparison to type 2b autoimmune CSU (P = 0.007) [Figure 4].

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Figure 4:

Box plot comparing elevated levels of serum immunoglobulin E in type 1 chronic spontaneous urticaria (CSU) in comparison to type 2 CSU. CRP: C-reactive protein.

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Furthermore, we found that angioedema was significantly associated with ANA positivity and higher UAS7 scores. Angioedema was also significantly more associated with the type 2b autoimmune type of CSU (P = 0.004). However, ASSTs did not have any significant association with the endotypes (P = 0.14).

DISCUSSION

Our findings are consistent with previous studies that reported a high prevalence of autoimmunity in CSU patients, especially in those who are resistant to conventional treatments.^[9] Autoimmune chronic urticaria is characterized by the presence of functional autoantibodies against various self-antigens, such as TPO, ANA, and FceRI. These autoantibodies can activate mast cells and basophils, leading to the release of histamine and other inflammatory mediators that cause urticaria and angioedema. The detection of these autoantibodies can help identify the endotypic variation and the severity of CSU.^[10,11]

However, the diagnostic methods for autoimmune CSU are not standardized and have limited availability and accuracy. The ASST is a simple and inexpensive test that can detect functional autoantibodies in CSU patients.^[12] However, the ASST has low sensitivity and specificity, and its results can vary depending on various factors, such as serum dilution, incubation time, and skin reactivity.^[11] Moreover, in our study, the ASST does not discriminate between different endotypes of CSU; therefore, we did not find it a reliable test to predict autoimmune CSU.

In our study, we used ELISA with standard commercial kits to detect the presence of autoantibodies against TPO and ANA, as these are some of the most common and relevant autoantigens in CSU patients. However, this method is also not without limitations. It requires specialized equipment and expertise, and it may not detect all types of autoantibodies or their subtypes. Furthermore, it may yield false-positive or false-negative results due to cross-reactivity or interference with other antibodies or proteins. Therefore, more sensitive and specific methods are needed to detect autoantibodies in CSU patients.

The UAS7 is a validated tool for measuring the severity of CSU based on the number and size of hives and the intensity of pruritus over 7 consecutive days. We found that autoimmune CSU was associated with higher UAS7 scores than autoallergic CSU. This suggests that autoimmune CSU is more severe and debilitating than autoallergic CSU.

We also found that angioedema was significantly associated with ANA positivity and higher UAS7 scores. Angioedema is a common manifestation of CSU that involves swelling of the deeper layers of the skin or mucous membranes. Angioedema can cause pain, discomfort, disfigurement, and even life-threatening complications if it affects the airway or gastrointestinal tract.^[12] The association between angioedema and ANA positivity may indicate the role of nuclear antigens or their complexes in triggering angioedema in some CSU patients.

According to a few studies, biomarkers for the cyclosporine response include basophil histamine release assay (BHRA) positivity, higher CRP levels, low total IgE levels, ASST positivity, low d-dimer levels, high disease activity, and short disease duration, whereas biomarkers for the omalizumab response include high levels of total IgE, ASST negativity, BHRA negativity, lack of basophil CD203c-upregulating activity, high expression of basophil FcRI, and lower interleukin-31 levels.^[13,14]

Our study provides new insights into the epidemiology and pathogenesis of CSU for Indian patients, a country with a high burden of allergic diseases but scarce data on this condition. Our study emphasizes the requirement to identify a subset of autoimmune CSU patients who may have a more prolonged and recalcitrant course. Although with the present algorithm of investigation, it may not be possible to unmask the entire gamut of autoimmunity in CSU, with simple laboratory tests such as a complete blood count, serum IgE, CRP, ANA, and anti-TPO antibodies, we may prognosticate the condition and choose appropriate therapeutic options.

However, our study also has some limitations that should be acknowledged. First, our sample size was small and may not be representative of the general population of CSU patients in India. Second, our study design was cross-sectional and did not allow us to assess the temporal relationship between autoimmunity and disease activity or impact. Third, our study did not include a control group of healthy individuals or patients with other skin disorders to compare the prevalence and specificity of autoantibodies. Fourth, our study did not evaluate the response to treatment or the prognosis of CSU patients with different endotypes. Therefore, further studies with larger sample sizes, longitudinal designs, and control groups are needed to confirm and extend our findings.

CONCLUSION

Our study provides new insights into the prevalence and endotypic diversity of CSU in India. While similar publications from other regions of the world have explored the autoimmune mechanisms in CSU, the prevalence of autoimmunity in the Indian context has been relatively underexplored. Our pilot data suggest that autoimmunity plays a significant role in CSU in our population, influencing disease severity and its impact. These findings highlight the need for standardized and accessible diagnostic tools for autoimmune CSU, as well as personalized treatment strategies for this complex condition. Further research is necessary to confirm and extend our findings and to explore potential therapeutic implications based on our results.