Leprosy, an infectious disease caused by Mycobacterium leprae (ML), causes immunological phenomena termed leprosy reactions that tend to increase following the initiation of multidrug therapy (MDT) and result primarily in neural damage1.
Leprosy reactions are divided into type one and type two reactions. Type one reactions are mediated by cellular immunity and involve the production of T-helper (Th) 1 response cytokines, including interferon-gamma, interleukin (IL)-2, and IL-122. Conversely, the type two reactions are characterized as systemic; they are related to the deposition of immune complexes and predominant Th2 responses, involving tumor necrosis factor-alpha (TNF-α), IL-6, IL-8, and IL-103.
The mixed reaction, which has a lower occurrence and has been rarely described in the literature, occurs mainly in the borderline lepromatous (BL) clinical form and is characterized by concurrent symptoms common to type one and two reactions4.
Since 1981, the World Health Organization (WHO) has recommended MDT for the treatment of leprosy, in order to fight bacterial infection5. However, the risk of developing reactions increases with the use of MDT due to the antimicrobial action of MDT, which causes the release of antigens that stimulate the occurrence of leprosy reactions by disrupting the mycobacterial cell wall6.
Assessing correlations between the number of reactions and variables that reflect the bacterial load, including the number of skin lesions, anti-phenolic glycolipid (PGL)-1 enzyme-linked immunosorbent assay (ELISA) serology, and bacterial indices (BIs) of skin biopsies and dermal smears, are important for clinical practice, since they help the team to monitor patients who will present as risk groups during treatment. Few studies have used the correlation between the number of reactions and clinical and laboratory data, as amounting leprosy reactions is not yet a routine practice in reference centers in Brazil or worldwide, and because there have been no surveys of health indicators related to leprosy reactions. Furthermore, it is clear that there is an absence of criteria to quantify the leprosy reactions and a lack of technology to support that procedure or to serve as a database for future research.
We aim to show the relationship between the number of leprosy reactions and the bacterial load represented mainly by bacterial indices of skin biopsies and dermal smear detected during the diagnosis.
Study and sample type
This is an observational cross-sectional study, consisting of 211 patients who presented with leprosy reactions during treatment and who were clinically classified according to the criteria of Ridley and Jopling7.
Data, collected through secondary sources (medical records) were predominantly epidemiological, clinical, and laboratory variables obtained for correlation analysis purposes. Extracted data included clinical and operational classification, the type of reaction, the number of leprosy reactions, time to the first reaction episode during treatment, the number of inspected skin lesions at diagnosis, and the BIs of dermal smears and skin biopsies.
Inclusion and exclusion criteria
This study included only patients with leprosy reactions during treatment with MDT at the National Reference Center for Sanitary Dermatology and Leprosy from January 2002 to December 2009. We excluded all patients with incomplete data, those who were transferred to other locations during treatment, and those with leprosy reactions at the time of diagnosis.
Criteria for clinical and operational classification
The clinical forms of patients included in the study were based on the classification suggested by Ridley and Jopling7, and included 7 groups, according to immunological, histological, and clinical characteristics, as follows: tuberculoid (TT), borderline tuberculoid (BT), borderline borderline (BB), borderline lepromatous (BL), subpolar lepromatous leprosy (LLs), and lepromatous lepromatous (LL). The operational classification was based on the criteria of the WHO together with other auxiliary methods, including laboratory tests used in the diagnosis, such as anti-PGL-1 ELISA serology, polymerase chain reaction analysis of dermal skin smears, peripheral blood analysis, skin biopsies, and the Mitsuda test.
Criteria for definition of leprosy reactions
Leprosy reactions (type one, type two, and mixed) were categorized based on clinical and immunological criteria described in the literature8.
Method of quantification of leprosy reactions
For the purpose of counting the number of reactions (type one, type two, and mixed), the following criteria were established: a new leprosy reaction was considered if symptoms were exacerbated at 7 or more days following completion of the reaction treatment, while a reaction was considered to be a continuation of the previous reaction (the same leprosy reaction) if symptoms were exacerbated in less than 7 days after completion of treatment. We propose this new methodology for counting the number of leprosy reactions, based on the time of the mean half-life of thalidomide (5.5 hours) for type 2 leprosy reaction (or mixed), the mean half-life of prednisone (3 hours) for type 1 leprosy reaction (or mixed), the reappearance of classical clinical signs related to leprosy reactions, and the absence of a consensus in the literature regarding calculating the number of leprosy reactions9) (10.
We used the non-parametric Spearman’s rank correlation coefficient test to assess the degree of association between the number of reactions during treatment and other clinical and laboratory variables. The statistical analysis was performed using GraphPad Prism, version 6 (GraphPad Software, Inc., La Jolla, CA, USA), and a significance level of p < 0.05 was assumed. Data were submitted to the D’Agostino-Pearson test to assess normality.
This study was approved by the Ethics Committee on Human Research of the Federal University of Uberlandia under the registration number 449/10 and protocol number 193/10. The ethical principles of this study support its methodology with the resolution of the National Health Council, number 466/2012.
This study involved 211 patients who developed leprosy reactions during treatment. As shown in Table 1, the BT (74/211; 35.1%) and LL (55/211; 26.1%) groups showed the highest frequencies among the clinical forms. The leprosy type 1 was seen in 64.5% (136/211) of patients, followed by the type two reaction, with 30.8% (65/211) of patients developing this type of immune response.
Table 2 shows the time to the first leprosy reaction following treatment initiation. Notably, the majority of reactions occurred within the first 3 months of treatment and the BT (68/211; 32.2%), BB (29/211; 13.7%), and LL (29/211; 13.7%) group patients presented with the earliest reactions during treatment. It is also noteworthy that 83.6% (46/55) of patients of the LL form showed reaction within the first year of treatment.
Table 3 shows the number of leprosy reactions per clinical form. The mean number of reactions during treatment was 1.6 per patient. However, the means of the LLs (2.6) and LL (2.1) groups were above 1.6.
There was a positive correlation between the number of leprosy reactions during treatment and the number of skin lesions inspected during the clinical diagnosis of the patients; however, the correlation was not significant (r = 0.24, p > 0.05).
Figure 1 shows a positive correlation between the number of leprosy reactions during treatment and the BIs obtained from skin biopsy samples at diagnosis (r = 0.20, p < 0.05). Although the correlation was considered weak, this association exists and did not occur at random.
Regarding the association between the number of leprosy reactions during treatment and the BI of dermal smears (Figure 2) in the same period, despite the correlation coefficient being weak (r = 0.21, p < 0.05), there was a positive correlation between these two variables, suggesting that an increase in the BIs of dermal smears may increase the number of leprosy reactions during treatment.
The high number of leprosy reactions seen in the first 3 months of treatment (155/211, 73.5%) was related to the effectiveness of MDT in the destruction of ML, mainly in multibacillary (MB), with a massive release of antigens following the initiation of therapy, remembering that >80% of leprosy patients were MB in a recent study11. The BT (74/211, 35.1%) and LL (55/211, 26.1%) clinical forms showed the highest frequencies among the clinical forms in this study.
The borderline group, consisting of BT, BB, and BL patients, represented the majority of patients in this study. These patients developed type one reactions only, with the exception of BL patients who developed type one, mixed, and type two reactions. This explains why the type one reaction had the highest incidence in this study, remembering also that this group, BT, BB, and BL, has a high immune instability and that, when bacteriological levels rise, bacterial load influences leprosy reactions, stimulating cell-mediated hypersensitivity phenomenon12. Patients with a high BI, such as those with the LL clinical form, have a greater risk of experiencing a reaction when the BI is >4, explaining the high number of type two reactions in the present study13.
As for the occurrence period of the first leprosy reaction during treatment, more than half of the patients had the first reaction within the first 3 months of treatment. This is consistent with studies reporting the occurrence of the type one reaction in the first 6 months, as observed in the borderline groups (BT and BB) as shown in our present study14. The borderline groups showed early reactions because of the large population of these individuals in the study. The LL clinical form, in our research, had a high number of subjects affected by leprosy reactions during the first year of MDT, triggered by the intense release of antigens in the blood flow leading to the formation of immune complexes within tissues15.
Few studies have quantified the number of leprosy reactions per patient. This is because of the difficulty in monitoring these individuals and the lack of criteria for determining the beginning and end of a reaction. In the present study, we calculated the mean number of reactions during treatment in more detail, similar to recent studies16) (17. In this study, the LLs and LL forms were more likely to develop reactions; both had a mean number of >2 leprosy reactions per patient during treatment3.
the non-parametric Spearman’s rank correlation coefficient detected a positive relationship between the number of leprosy reactions during treatment and the number of skin lesions inspected in the clinical diagnosis of patients. Few studies have evaluated this relationship directly, although another study did detect a relationship between the occurrence of leprosy type one reactions and the size of the lesion, in which lesions of >5cm were a risk factor18. This study showed that 59.4% (44/74) of borderline tuberculoid patients were multibacillary, which explains how an increased BIs and skin lesions can be risk factors for type one reactions19.
A positive correlation between the number of leprosy reactions during treatment and the BIs of skin biopsies collected at diagnosis was demonstrated by the Spearman’s correlation analysis, which indicated a weak, but statistically significant correlation. The BIs of biopsies reliably indicates the bacterial load of patients, which, in turn, is predictive for the occurrence of reactions, as cited in recent studies on the analysis of the correlation between anti-PGL-1 ELISA serology diagnosis and the number of reactions during treatment, since this also refers to the amount of antigen present in individuals16) (17) (20.
Similar to the BIs of skin biopsies, the BIs of dermal smears was associated with the number of leprosy reactions during treatment, indicating a strong influence again of the bacterial load on the outcome of leprosy reactions. This fact was quoted in a study about the association of leprosy reactions and the bacterial load, which calculated odds ratios to measure the chance of patients with a positive initial dermal smear developing a leprosy reaction during and/or following treatment. The study found a result of 2.94, although it was not statistically significant21.
The relationship between bacterial load and the number of leprosy reactions during treatment, represented in the present study by the BIs of dermal smears and skin biopsies, showed a weak correlation in this sample; however, the scientific community recognizes these associations through other studies16.
In conclusion, this study about leprosy reactions during treatment showed that clinical and laboratory data can help to identify risk groups and create monitoring protocols for these patients, preventing neural injury and secondary infections.