Leprosy is a disease known since ancient times. Historical depictions have contributed over the years to strengthening the rejection, prejudice, and social exclusion experienced by individuals suffering with leprosy.1 In 1873, Gerhard Armauer Hansen identified Mycobacterium leprae, an obligate intracellular parasite with affinity for skin and peripheral nerves.2,3 Currently, Brazil has the second highest number of cases of this disease, being surpassed only by India.4

The major control measure for this endemic disease was the implementation of multidrug therapy (MDT) in endemic countries by the World Health Organization (WHO) in 1982. This therapeutic program established the criteria for treatment success and cure. However, if the patient already had neural deficit at the time of diagnosis, it may remain as a sequela even after bacterial inactivity. This deficit is a consequence of nerve damage.

The sensory nerve damage in leprosy is characterized by two distinct clinical situations: one is the direct impairment of fine nerve endings and sensory corpuscles by M. leprae, wherein the loss of function is slowly progressive, from a clinical perspective. The other clinical manifestation of neuropathy is the impairment of peripheral nerve trunks.5

In the case of hand impairments, decreased sensibility as well as deformities caused by muscle weakness due to leprosy, may contribute to the reorganization of the somatosensory cortex of the brain due to the decreased input of stimuli to the central nervous system. These modifications lead to individual synaptic changes, causing the reorganization of specific brain areas, such as the primary somatosensory cortex (S1), which ultimately result in functional consequences, such as altered recognition and changes in motor control.6–10 The representation of the body in the brain (somatotopic map) relies on S1.11 However, the body’s awareness goes beyond the S1 cortical body map and includes the body’s spatial representation and the surrounding environment (peripersonal space).12 The ‘body schema’ can be understood as a multisensory representation that is likely to receive inputs from several brain areas that code for visual, tactile, and proprioceptive inputs.12

Neuroplastic changes have been observed in S1 in the ‘phantom limb’ sensation (i.e., sensation that an amputated or missing limb is still attached). This happens because the somatotopic map previously linked, for example, to the arm, instead of becoming invalid after amputation, starts representing neighboring areas, causing stimuli in these areas to be interpreted as coming from the arm. In phantom limb phenomena, there is cortical reorganization with expansion of areas adjacent to the previously occupied area. Sensory loss in leprosy is believed to result in a similar phenomenon. Gradual and slow absorption of fingertips in leprosy is likely accompanied by a gradual and simultaneous cortical reorganization process, which does not result in phantom limb or phantom pain phenomena. In addition, the digits or adjacent parts are also anesthetized, and their areas of representation are already reduced.13

The laterality judgment task or left/right judgment task (LRJT) is based on images representing a body segment, where the participant is requested to judge which side of the body the image belongs to with accuracy and with the shortest response time. During the LRJT, the participant performs a mental body rotation and compares the image with their body representation in the brain.14 Thus, a reduction in accuracy is thought to reflect an affected body schema.15 Findings from a study by Price demonstrated that the phantom limb phenomenon can be found both in people who underwent limb amputation and in patients with shortened fingers or toes, other limb deformities, such as claw hand, and sensory and motor loss even without significant loss of tissue, as in patients with leprosy.16 Thus, due to the sensory and motor impairment occurring in leprosy that consequently decreases inputs to the brain, it is possible that people with this disease may have difficulty in identifying the affected segment during a task of side recognition. This study aimed to investigate the ability of patients with nerve damage caused by leprosy to distinguish left and right, compared with that of a control group.

This was an observational study, with a cross-sectional design. We included patients with a diagnosis of leprosy and grade 1 physical disability (GD1) and excluded patients with pain or other peripheral neuropathies, results lower than those predicted in the Mini-Mental State Examination, or decreased muscle strength, in addition to those who did not understand the execution of the test and/or reported being ambidextrous. Patients with grade 2 physical disability was not considered eligible since motor deficits would influence the response in the laterality judgment task. The assessment protocol comprised an instrument for collecting sociodemographic and clinical data. In the physical examination, sensory-motor evaluation, assessment of handedness (hand predominance), and mental status assessment were performed.

The laterality judgment task was performed using the ‘Vanilla’ option of the Recognise HandTM application (Neuro Orthopedic Institute, NoiGroup, Adelaide AS, AUS), installed on a 9.7-inch tablet with display resolution of 768 ×1024 pixels (Ipad 2, Apple, California, USA). The ‘Vanilla’ difficulty setting images of the body region are presented against a plain background, randomly rotated at 0, 90, or 180 degrees to either the left or right. In this study, the images were of hands in various positions and the subject decides whether the hand being shown is the left or right hand. Each image was displayed in random order at five seconds intervals, and a new image was shown if no selection was made, to a total of 40 images. Participants were instructed to make their judgments as fast and accurately as possible. Before the test, participants were submitted to a familiarization protocol using 20 images of the foot. These results were compared to the responses of a control group that was composed of healthy individuals. Normality was set at 80% accuracy.

The data were digitized in an electronic spreadsheet and then analyzed using the software Statistical Package for the Social Sciences (SPSS) version 20. The study population was characterized via an analysis of the measurements of frequency, central tendency, and dispersion (means, standard deviations, minimum values, maximum values, and confidence intervals). Mean accuracy was compared between the groups using Student’s t-test. Significance was set at p ≤ 0.05. Correlation of the variables time since diagnosis × sensibility, time since diagnosis × accuracy, age × accuracy, sex × accuracy, and sensibility × accuracy was analyzed using Fischer’s exact test as an exercise of possibilities.

This study respected the ethical recommendations contained in CNS/MS resolution no. 466/12 and was previously submitted to and approved by the Research Ethics Committee of the University Hospital of the Federal University of Rio de Janeiro (CAAE: 73455417.0.0000.5257). After obtaining the approval and registration, the survey was initiated. All patients who agreed to participate in the study were duly informed and signed two copies of an informed consent form, one copy for the participant and the other for the researcher.

Thirty-three individuals were recruited for the study, including 20 patients diagnosed with leprosy (patient group), classified with grade 1 disability (exclusively sensory impairment) and 13 healthy individuals (control group). Of the 20 individuals in the patient group, 7 were excluded because they presented sensory loss in only one hand. The final study sample consisted of 13 patients, 6 male and 7 female, with a mean age of 53 years (xmin = 33; xmax = 83; SD = 15.9). The time since diagnosis of leprosy was on an average 100 months (xmin = 3; xmax = 267; SD = 79.4) and the average time since MDT discontinuation was 86 months (xmin = 0; xmax = 246; SD = 76.7). The control group consisted of 13 individuals, 6 males and 7 females with a mean age of 53 years (xmin = 30; xmax = 78; SD = 16.1), who were paired by gender and age with the individuals in the patient group.

Table 1 presents the data of each patient on the time since diagnosis, sensibility, and accuracy. The subjects were grouped based on their time since diagnosis (in months), with group 1 being composed of individuals with up to 40 months since diagnosis, group 2 being individuals with 41 to 151 months, and group 3 being diagnosed 152 months or more previously. Sensibility values can vary from 0 to 30, the higher the value, the closer to normality.

For the patient group, the laterality judgment task had an average accuracy of 70% for the right hand (xmin = 35; xmax = 100; SD = 20.3; 95% CI = 57.7–82.2) and 62% for the left hand (xmin = 30; xmax = 100; SD = 25.5; 95% CI = 46.8–77.7). In the control group, the accuracy was 83.4% for the right hand (xmin = 60; xmax = 100; SD = 11.4; 95% CI = 76.5–90.3) and 83.8% for the left hand (xmin = 60; xmax = 95; SD = 9.1; 95% CI = 78.3–89.3). Figures 1 and 2 represent the data referring to the distribution of mean accuracy of the patient and control groups.

Although the sample size does not allow us to make inferences on the influence of clinical diagnostic factors on sensibility and accuracy, the individuals with longer periods since diagnosis seemed to show better results regarding the sensibility of both hands when compared to the individuals with a more recent diagnosis. Time since diagnosis also did not seem to influence accuracy in both hands. Regarding age, the youngest group showed a tendency to have better accuracy than the others, with results above 60% for both hands in all individuals of the group. Additionally, female subjects presented better accuracy in the right and left hands in the patient group (Table 1).

The control group presented an average accuracy of 83%; however, men appeared to have better accuracy in the right hand, whereas women performed better with the left hand. Age did not seem to influence the accuracy of individuals in the control group (Table 2).

Although individuals with sensory deficit presented lower accuracy than those of the control group, the degree of sensory impairment did not appear to be proportionally related to the quality of performance in the test, i.e., individuals with worse sensibility were not those with the worst performance (Tables 3 and 4).

The hypothesis tested in this study was that altered sensibility is associated with lower performance (accuracy) in the laterality judgment task in people affected by leprosy in comparison to healthy controls. The results showed a compromised accuracy for the laterality judgment task in patients diagnosed with leprosy and with altered hand sensibility. For this analysis, we used a patient group and a control group that included healthy individuals, without neural impairment or deformities of the hands. The control group presented an accuracy of 83.4% for the right hand and 83.3% for the left hand. These results are in accordance with those of a study by Moseley et al. (2012),17 who evaluated 6 normal individuals and observed an average of 80% accuracy for both hands. This value is considered the normality parameter for this test according to the NOI Group, developer of this protocol.

In our study, the patient group presented results below these values, with a mean accuracy of 70% for the right hand and 62% for the left hand. These findings were even lower than those found in the above-cited study,17 wherein the laterality judgment by individuals with complex regional pain syndrome was evaluated in two centers specialized in the management of these patients. Accuracy was lower for responses involving recognition of the affected side than for the recognition of the unaffected side. Additionally, there was a difference in the responses of patients between the two specialty centers. In research center 1, a rate of 66.3% correct responses was observed for the affected side and 77.6% for the unaffected side. Research center 2 presented a rate of 75% correct responses for the affected side and 80.9% for the unaffected side. It is possible that the lower values observed in this study, as compared to the aforementioned study that evaluated unilateral impairment, are a result of bilateral involvement in the patients of this study.

Time since diagnosis and level of sensibility did not interfere with the accuracy results. As observed in this study and stated in the literature, it is possible that peripheral nerve damage contributes to changes in the sensory cerebral cortex. In a study that used transverse section of the median nerve, changes in the cerebral somatosensory cortex corresponding to the median nerve representation areas were observed. The adjacent cortical areas were found to quickly expand and occupy the former area of the median nerve.18,19 These changes occur within minutes and are possibly based on the inhibition of synaptic connections.20 This data explains why the difference in time since diagnosis did not interfere with the results of accuracy in our study.

The study by Schwoebel et al.21 demonstrated that, in people with unilateral complex regional pain syndrome, the time to recognize right or left is longer when the image coincides with the affected hand than when it coincides with the unaffected hand, but the difference decreases when pain subsides. Because our study evaluated individuals with bilateral lesions, the results from our study could not be compared to those found by these authors.

In our research, Figures 1 and 2 demonstrate that the data of the control group individuals was closer to the mean of this group, whereas the data of the patient group was more heterogeneous. We also observed that the images of right hand (70%) in the patient group were generated with greater accuracy than those of the left hand (62%). This may have resulted from the participants being right-handed and the effects of the dominant hand and visual familiarity being in agreement, i.e., the greater use of the right hand results in greater familiarity with the right hands of other individuals.22,23

Peripheral nerve lesions remain as disabilities and are one of the most challenging surgical reconstruction problems, especially in the case of hands. Nerve lesions can seriously interfere with an individual’s ability to perform their functions properly, and the acquired disability is often dramatic: a hand without sensibility is usually a hand without function.20 This evidence could explain our results regarding the lower accuracy of patients when compared with the individuals of the control group.

It is important to highlight the results of our study, because, until now, research addressing the topic of laterality judgment has been carried out mainly in situations of absence of limbs (amputations) and in cases of chronic pain, such as in type 1 complex regional pain syndrome. We found no studies assessing side recognition of hands in people with progressive peripheral nerve lesions, such as those in leprosy.

One of the potential clinical applications of this research is that, in cases of patients with leprosy, surgeries and/or physical therapy can be performed to correct hand deformities (claw hands) to keep the limb as functional as possible. Thus, this study on laterality judgment task can contribute to both rehabilitation process of patients and monitoring of their progress. The rehabilitation success of patients who underwent tendon transfer surgical intervention for the correction of claw hands, for example, can be compromised if they do not recognize the operated limb.7

A potential use of this study would be to perform side recognition test before and after tendon transfer surgery, as this procedure aims for motor and functional gain rather than sensory gain. Thus, it is interesting to investigate the extent to which improving function can represent an improvement in cortical representation, even without any sensory improvement. Perhaps, even in patients not undergoing hand repair surgeries, we can find results that aid in monitoring patients while exercising self-care and in the process of re-education, which aim to improve protective actions that have been lost by numbing of these areas. As this test is also used in clinical practice for training cortical representation of an injured limb in individuals with unilateral lesions, it is possibly applicable to individuals with bilateral definitive lesions, as it helps in the preservation of the body schema.

Patients with sensory hand impairment showed lower accuracy in the task of side recognition than individuals in the control group. The accuracy results obtained in the study indicate alteration in the laterality judgment task, which is possibly related to peripheral nerve damage. These changes may be indicative of changes to the representations in the area corresponding to the hand in the brain’s primary sensory cortex.

Considering the low number of participants in the current study, the results presented here can be considered preliminary. Clinicians should be aware that patients affected by leprosy with disability Grade I may present deficits in the recognition of hands. Difficulties in recognizing a body segment can impact on motor control. In leprosy, this finding can be relevant since patients are submitted to hand rehabilitation programs and surgery such as tendon transfer and claws corrections. Future researches should investigate the laterality judgment task with a larger sample size and also consider other sensory assessments such as the two-point discrimination test. It is recommended that neuroplastic changes in the brain be investigated in neuroimaging studies to quantify anatomical and functional brain changes in people affected by leprosy with different levels of physical disabilities. Besides, clinical studies should also clarify if laterality judgment training can improve functional outcomes.

This is study is not free of limitation. The main limitation was the sample size. The restricted number of patients included in this study may be explained since they were recruited in a tertiary referral center. Most patients are referred to our center due to disability Grade 2 to be submitted to surgical correction (drop foot, claw hands) and rehabilitation programs. Lastly, the laterality judgment task, as related in the literature in some clinical conditions, can suggest neuroplastic changes in the brain; but it is an indirect inference. Moreover, performance on the laterality judgment task might be influenced by cognitive deficits (e.g., attentional bias, disturbances in decision-making process, and psychomotor speed) in persons with leprosy, which still need to be clarified.