High-Resolution Sonography as an Additional Diagnostic and Prognostic Tool to Monitor Disease Activity in Leprosy: A Two-Year Prospective Study

Abstract

Purpose Early diagnosis and treatment of leprosy and leprosy reactions are essential to prevent stigmatizing deformities and disability. Although the incidence of leprosy has decreased enormously, grade 2 disability due to nerve injury has remained the same. New tools are needed to better diagnose and monitor leprosy reactions and associated neuritis and this study assessed whether high-resolution sonography (HRUS) can be used as such a tool.

Materials and Methods During a prospective follow-up period of 2 years at regular intervals, we performed clinical examination to assess sensory and motor function and HRUS of the four main peripheral nerves in 57 patients, of whom 36 were with reactions and 21 were without reactions. Normative data of the cross-sectional area (CSA) of these nerves were obtained from 55 healthy subjects (HS). Color Doppler (CD) was used to study blood flow in the nerves.

Results At the baseline visit and during follow-up, all four nerves were significantly thicker in patients with leprosy reactions in comparison to HS (p < 0.0001) and to a lesser extent also in comparison to patients without reactions ranging from a p-value of < 0.05 to < 0.0001 in the different nerves tested. During follow-up, the nerve size did not change significantly in patients without reactions, while it decreased significantly in patients with reactions. At baseline, endoneural blood flow was present only in patients with reactions. This occurred in 20 of the 36 (55 %) patients (49 nerves) and decreased to only 1 patient (2.7 %) at the end of the follow-up period.

Conclusion This prospective study demonstrates the ability of HRUS to monitor disease activity and the effect of treatment in patients with leprosy reactions by determining changes in nerve size and vascularity, which are indicators of peripheral nerve involvement and damage.

Zusammenfassung

Ziel Frühe Diagnose und Therapie der Lepra und der Lepra-Reaktionen ist entscheidend, um stigmatisierende Entstellungen und Behinderungen zu verhindern. Obwohl die Lepra-Inzidenz immens gesunken ist, ist eine Behinderung 2. Grades aufgrund der Nervenschädigung gleich häufig geblieben. Neue Verfahren für eine bessere Diagnose und Überwachung der Lepra-Reaktionen und der assoziierten Neuritis sind erforderlich, daher überprüft diese Studie, ob HRUS hierfür eingesetzt werden kann.

Material und Methoden Während eines prospektiven Nachuntersuchungszeitraums von 2 Jahren mit gleichmäßigen Intervallen führten wir bei 57 Patienten eine klinische Untersuchung der sensorischen und motorischen Funktionen und HRUS der vier peripheren Hauptnerven durch, von denen 36 Reaktionen und 21 keine Reaktionen zeigten. Die normativen Werte der Querschnittsregion (CSA) dieser Nerven wurden bei 55 Gesunden erhoben. Farbdopplersonografie wurde durchgeführt, um den Blutfluss in den Nerven zu ermitteln.

Ergebnisse: Beim Erstbesuch und während der Folgeuntersuchungen waren bei allen Patienten mit Lepra-Reaktionen im Vergleich zu gesunden alle vier Nerven signifikant dicker (p < 0,0001) und in geringerem Maße auch im Vergleich zu Patienten ohne Reaktionen, die in einem p-Wert-Bereich zwischen < 0,05 und < 0,0001 für die verschiedenen untersuchten Nerven lagen. Während der Folgeuntersuchungen veränderte sich bei Patienten ohne Reaktion die Größe der Nerven kaum, während sie bei Patienten mit Reaktionen signifikant kleiner wurden. Bei Erstaufnahme war der endoneurale Blutfluss nur bei Patienten mit Reaktionen vorhanden, dies traf für 20 (55 %) der 36 Patienten zu (49 Nerven) und sank auf nur einen Patienten (2,7 %) am Ende des Nachsorgezeitraums ab.

Schlussfolgerung Diese prospektive Studie zeigt die Möglichkeit des HRUS, die Erkrankungsaktivität und den Therapieerfolg bei Patienten mit Lepra-Reaktionen zu überwachen, indem die Veränderungen der Nervengröße und Durchblutung bestimmt werden, welche Hinweise auf eine Beteilung der peripheren Nerven und deren Schädigung geben.

Key words

high-resolution ultrasonography - peripheral nerves - leprosy - reactions - grade 2 disabilities

Introduction

Leprosy caused by Mycobacterium leprae is the most common treatable infectious disease of the peripheral nervous system. The key features of leprosy are the involvement of the skin and peripheral nerves leading to a chronic granulomatous immune response and peripheral neuropathy in a proportion of patients who experience leprosy reactions [1]. M. leprae residing in macrophages and Schwann cells cause inflammation, nerve enlargement and extensive demyelination of peripheral nerves. Although the incidence of new cases has decreased in India, grade 2 disability due to peripheral nerve damage with clinical deficits and deformity has remained the same [2] [3].

The main method of leprosy diagnosis is clinical: the identification of typical hypo-pigmented anesthetic skin patches, peripheral nerve palpation, testing for sensory loss by sensory testing (ST) and muscle weakness by voluntary muscle testing (VMT) along with histopathological confirmation. Peripheral nerve damage occurs due to the direct invasion of M. leprae into the nerves resulting in reactional states (Type 1 & 2) due to an inflammatory process which is intense and irreversible [4]. Early diagnosis and treatment of peripheral neuropathy are essential to prevent stigmatizing deformities and disabilities in leprosy. Diagnosis of leprosy reactions and underlying nerve injury would help to reverse the damage with prompt treatment.

High-resolution ultrasonography (HRUS) has rapidly gained popularity as a noninvasive tool in the evaluation of the peripheral nervous system. HRUS provides useful information on the location and degree of nerve enlargement, alterations in nerve morphology, echotexture, vascularity and fascicular pattern that helps in the modification and enhancement of differential diagnosis and treatment of peripheral nerve disorders [5] [6] [7]. This noninvasive tool brings a new dimension to the diagnosis of leprosy and its reactions. The increased blood flow and vascularity observed in ultrasound (US) have been associated with the inflammatory process and therefore ultrasound could be a tool for determining the need to initiate corticosteroid therapy to prevent/treat the nerve damage associated with reactions. Until now there have not been any prospective studies using ultrasound for monitoring disease activity in polyneuropathies. Therefore, we decided to assess whether HRUS can be used to monitor disease activity in patients with leprosy reactions and compare this data with leprosy patients without reactions during a follow-up period of 2 years.

The objectives of our study were 1) to evaluate and compare the extent and difference of peripheral nerve damage as assessed by clinical examination (clinical grading of nerve enlargement, sensory loss and VMT) and HRUS [cross-sectional area (CSA), endoneural flow (EF), and echotexture (ET)] in patients with leprosy reactions and patients without reactions and to compare these findings with healthy subjects and 2) to assess whether HRUS is a useful tool to monitor changes in the size and blood flow of nerves as indicators of nerve injury in reactions and also to monitor their response to corticosteroid treatment.

Materials & Methods

Study population

A total of 57 leprosy patients were enrolled including 21 without reactions (C) and 36 with reactions (R) (21 patients with type 1 and 9 with type 2 reaction) ([Table 1]). All patients were adults except for two who were children aged 12 and 13, classified according to the Ridley Jopling criteria [8] and were on WHO multi-drug therapy (MDT), with and without prednisolone treatment and evaluated at CODEWEL Nireekshana ACET, Hyderabad with HRUS at the first presentation to the clinic. Prior approval from the institution’s ethical committee and informed consent from the patients was obtained. Patients with reactions were started on 40 mg of prednisolone per day which was tapered over 6 months to 5 mg per day. A leprologist, who was blinded to the results of ultrasound, assessed the nerve thickening of the patient independently and graded the thickening. Patients with associated diseases which could cause nerve thickening or nerve function impairment or neuropathy were excluded. HRUS was performed at baseline (0 months) and at 3, 6, 12, 18 and 24 months of follow-up.

Table 1 Profile of leprosy patients (n = 57) enrolled in the study.

		leprosy without reactions (C = 21)								leprosy with reactions (R = 36)
S. No	type	BT(13)		BL(1)		LL(5)		PNL(2)		BT(16)		BB(1)		BL(4)		LL(9)		PNL(6)
	sex	m	f	m	f	m	f	m	f	m	f	m	f	m	f	m	f	m	f
		9	4	1	–	3	2	2	–	15	1	1	–	3	1	7	2	5	1
		age in years
1	mean	22		26		39.2		46.5		32.7		22		33.8		27		36.8
2	median	26		26		40		46.5		30		22		29		24		34.5
3	range	12 – 28		26		27 – 50		45 – 48		18 – 57		22		13 – 52		28 – 52		22 – 45
		duration of disease in months
1	mean	15.3		6		61.4		8		24.7		8		20		21.1		6
2	median	7		6		12		8		21		8		21		12		3.5
3	range	1 – 60		6		1 – 240		5 – 11		1 – 84		8		2 – 36		1 – 66		1 – 24

BT-Borderline Tuberculoid; BB-Borderline Borderline; BL-Borderline Lepromatous; LL-Lepromatous Leprosy; PNL- Pure Neuritic Leprosy.

Healthy subjects (HS) were clinically and sonographically assessed only once during the study at the time of enrollment to compare the CSAs of the healthy nerves with the nerves of the leprosy patients.

Clinical evaluation/grading of nerve

All patients and healthy subjects were examined by a technician trained in leprosy to bilaterally assess the ulnar (UN), median (MN), lateral popliteal or fibular (LP (FN)) and posterior tibial (PT) nerves, as described earlier [5]. All the nerves were examined with regard to their motor and sensory functions as follows. For sensory testing Semmes-Weinstein monofilaments (SW) were used as previously described [9] [10]. Muscle weakness was assessed using the Medical Research Council (MRC) [11] grading.

1) UN: Each patient was screened for current symptoms of lesions of the UN, i. e. numbness and paresthesia of the fourth and fifth digits of the hand, medial elbow pain, weakness or clumsiness of the hand muscles innervated by the UN. Both arms were examined by testing (1) pin-prick sensation at digit 5 using monofilaments, and (2) strength of the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) using the MRC rating scale.

2) MN: We evaluated sensation in the distribution of the MN using monofilaments and assessed the motor function of the abductor pollicis brevis (APB).

3) LP: The strength of the extensor hallucis longus and tibialis anterior was tested using the MRC rating scale and sensory testing was performed using monofilaments.

4) PT: Current symptoms of lesion of the PT nerve were tested for the muscle strength of the toe and foot flexors and sensation at the heel and sole of the foot using monofilaments.

The UN, LP and PT were clinically graded after palpation as follows: Grade 0: the nerve was not thicker than the contralateral nerve and with normal sensation; Grade 1: the affected nerve was thicker than the contralateral nerve; Grade 2: the thickening of the affected nerve felt rope-like; Grade 3: a thickened nerve felt beaded or nodular. Clinical grading of nerve thickening based on palpation could not be performed on MN due to its deeper location.

Skin smears were taken from three sites (the earlobe, forehead and skin patch or area of anesthesia) for the presence of acid-fast bacilli and to assess the Bacillary Index (BI). Skin biopsies were performed to confirm the clinical diagnosis in a proportion of the patients. Skin smears were positive in 17 patients (4 in controls and 13 in reactions) with a range of 0·25 to 4·6. Two control patients, i. e., without reactions, were smear negative possibly because they were treated in the past.

Definition of clinical neuritis/nerve damage

We defined nerve function impairment (NFI) in terms of ‘sensory loss’ when the patient was unable to perceive 2 grams of target force on the hand using SW filaments and 20 grams on the foot at any one of the three sites tested for each nerve and ‘motor weakness’ when the voluntary muscle testing (VMT) score was ≤ 4.

HRUS assessment

Imaging of the nerves was done using HRUS along with color Doppler (CD) (Esoate — MyLab 5 color Doppler system, The Netherlands) with a linear array transducer with a broadband frequency of 6 – 18 MHz (LA435). In brief, four nerves (UN at the elbow and proximal to the medial epicondyle, MN at wrist, LP at the fibula head and PT at the ankle and proximal to the medial malleolus) of the patients were examined bilaterally at baseline and followed up at 3, 6, 12, 18 and 24 months. The evaluation consisted of measurement of the maximum cross-sectional area (CSA) in mm² and the nerve echotexture and detection of endo- and epineural color flow signals as described in detail previously [5]. On transverse scans, the CSA of the nerve was determined from that area by one measurement within the hyperechoic rim surrounding the nerve. The echo reflectivity of the nerves assessed on imaging was arbitrarily graded as follows: mild = some hypo-reflectivity; moderate = obvious hypo-reflectivity; and severe = absence of any fascicular pattern.

Color Doppler (CD) settings were chosen to optimize the identification of weak signals from vessels with slow velocity. The pulse repetition frequency was set at 0.7 KHZ and the Doppler gain was adjusted to the maximum levels in order to reduce signal noise. The band filter was set at 50 Hz. The presence of blood flow signals at the epineurium or intraneural blood vessels indicated hypervascularity of the nerve during CD imaging and was recorded as present or absent and not quantified. Any flow signal was taken as an indicator of acute reaction in the nerve. The absence of blood flow signals during follow-up was taken as a good response to steroid treatment.

Statistical analysis

Statistical analysis was performed using SAS software version 9.1.3 and GraphPad prism version 6. For comparison of group differences, the one way non-parametric analysis of variance Kruskal-Wallis or Wilcoxon-Mann-Whitney tests were used, and the Fisher Exact test (X²) was used for comparison of proportions. Probability (p) values less than < 0.05 were considered significant.

Results

Baseline characteristics

Healthy subjects

The previously mentioned nerves were examined clinically and assessed by HRUS bilaterally in 55 healthy adult subjects (HS) (males = 30 and females = 25) to obtain normal values for the HRUS parameters. Clinical examination via nerve palpation showed all the nerves of the upper and lower limbs to be of normal size, without enlargement and tenderness. On HRUS, all of these nerves showed well-defined fascicles (round to oval with occasional honeycomb pattern in cross-sectional view and as bundles of straw in longitudinal view), normal echotexture, with absence of endoneural and epineural blood flow signals on CD imaging. The median CSA value in the UN, MN and PT was 6 mm² and that of the LP was 7 mm².

Patients

Of the 57 patients, 21 were without reactions (C) and 36 were with reactions (R) and all were followed up for 2 years. Classification, type of reaction, age, sex and duration of disease of these 57 patients are shown in [Table 1].

[Table 2] shows the mean ± SD of the CSAs of the different nerves by HRUS in leprosy patients without reactions (C = 21), leprosy with reactions (R = 36) vs. healthy subjects (n = 55). The nerves were significantly thicker in the leprosy patients as compared to healthy subjects (p < 0.0001). The arm nerves were relatively more thickened than the leg nerves.

Table 2 Follow-up (0 – 24 months) of cross-sectional area (CSA in mm²) of bilateral UN, MN, LP & PT nerves in leprosy patients without reactions (C = 21) and with reactions (R = 36). In healthy subjects (HS), the CSA was assessed only at month 0 (baseline).

subjects	ulnar nerve (UN)	median nerve (MN)	lateral popliteal nerve (LP)	posterior tibial nerve (PT)
healthy subjects (HS = 55)
0 months (55)
mean ± SD	7.03 ± 3.18	6.68 ± 1.98	7.42 ± 2.5	6.93 ± 3.20
leprosy without reactions (C = 21)
0 months (42)[1]
mean ± SD	12 ± 9.5	10 ± 4.5	7.25 ± 2.9	9.6 ± 3.6
p-value[2]	0.0002	< 0.0001	NS	< 0.0001
3 months (42)
mean ± SD	9.8 ± 6.4	9.7 ± 3.7	7.4 ± 2.9	9.6 ± 4.8
6 months (42)
mean ± SD	9.6 ± 5.5	9.6 ± 3.6	7.7 ± 2.9	9.4 ± 4.8
12 months (42)
mean ± SD	10 ± 5.9	9.9 ± 4.8	8.2 ± 3.8	11 ± 6.2
18 months (42)
mean ± SD	9.4 ± 4.6	9.1 ± 3.9	7.9 ± 3.1	10 ± 4.2
24 months (42)
mean ± SD	9.1 ± 7	8.5 ± 3.3	9.1 ± 8.1	11 ± 5.2
leprosy with reactions (R = 36)
0 months (72)1
mean ± SD	20 ± 19	17 ± 14	13 ± 8.5	14 ± 9.2
p-value[3]	< 0.0001	< 0.0001	< 0.0001	< 0.0001
p-value[4]	< 0.0001	0.024	< 0.0001	NS
3 months (72)
mean ± SD	19 ± 17	12 ± 6.4	11 ± 7.3	13 ± 7.4
p-value4	< 0.0001	0.089	0.0002	0.0034
6 months (72)
mean ± SD	19 ± 16	15 ± 9	12 ± 5.9	14 ± 7.8
p-value4	< 0.0001	< 0.0001	< 0.0001	0.0002
12 months (72)
mean ± SD	16 ± 15	11 ± 5.3	12 ± 7.8	14 ± 6.1
p-value4	< 0.0001	NS	0.0003	0.0025
18 months (72)
mean ± SD	17 ± 13	12 ± 5.2	10 ± 5.7	12 ± 5.9
p-value4	< 0.0001	0.0011	0.0073	0.0452
24 months (72)
mean ± SD	15 ± 12	11 ± 4.1	10 ± 5.5	12 ± 6
p-value4	< 0.0001	< 0.0001	NS	NS

NS – Not Significant.

¹ Number of nerves tested.

² Healthy subjects (HS) in comparison with leprosy without reactions (C) (p < 0.0001).

³ Healthy subjects (HS) in comparison with leprosy with reactions (R) (p < 0.0001).

⁴ Leprosy without reactions (C) in comparison with leprosy with reactions (R) (p < 0.05 to p < 0.0001).

At the baseline visit, all 4 nerves were significantly thicker in patients with reactions (R) and in patients without reactions (C) when compared to healthy subjects (p < 0.0001), except for the LP in the case of leprosy without reactions (C). [Table 2] shows the mean CSAs of the different nerves in patients without reactions (n = 21) versus patients with reactions (n = 36). Except for the PT, all of the other nerves were significantly thicker in patients with reactions when compared to patients without reactions (p = 0.024 to p < 0.0001).

Follow-up data

During the 24-month follow-up of the CSAs, the UN showed significantly greater thickening in every month (p < 0.05 to p < 0.0001) when compared to the MN, LP and PT (in patients without reactions (C) versus patients with reactions (R)). The maximum CSA of the UN was observed at baseline and showed a significant decrease during the follow-up in clinically affected (presence of NFI) and unaffected (absence of NFI) nerves in patients without reactions and with reactions ([Table 2, ] [Fig. 1a, b]). A decrease in nerve size during follow-up was also seen in the other three nerves. All four nerves exhibited different peaks and troughs of the CSA on the right and left side and showed a marked reduction in nerve size during steroid treatment. An example is shown in [Fig. 2]. HRUS findings of a case with reactions ([Fig. 3]) showed marked fluctuations in the CSA of the UN nerve with prednisolone treatment when compared to the other three nerves. All nerves in patients with reactions showed an increased CSA when compared to healthy subjects. However, patients without reactions ([Fig. 4]) showed no change during the follow-up in comparison with patients with reactions. During follow-up, the nerve size did not change substantially in patients without reactions, while it decreased significantly in patients with reactions (p < 0.0001). The functional status of the nerves did not change in patients without reactions (C) during follow-up.

Fig. 1 a Scatter gram showing follow-up (0, 12 & 24 months) of cross-sectional area (CSA in mm2) in UN and MN nerves [(unaffected (UA) and affected (A)] between leprosy patients without reactions (C = 21) & with reactions (R = 36). Dotted line is the mean + two SD of healthy subjects. b Scatter gram showing follow-up (0, 12 & 24 months) of cross-sectional area (CSA in mm2) in LP and PT nerves [(unaffected (UA) and affected (A)] between leprosy patients without reactions (C = 21) & with reactions (R = 36). Dotted line is the mean + two SD of healthy subjects.

Fig. 2 A representative graph of a patient with reaction showing different peaks and troughs of cross-sectional area (CSA in mm2) of bilateral UN, MN, LP and PT nerves during follow-up (0 – 24 months).

Fig. 3 Ultrasonography images of follow-up (0 – 24 months) of cross-sectional area (CSA in mm2) of UN, MN, LP and PT nerves of leprosy with reaction (R) in comparison to healthy subject (HS) at 0 months. Ulnar nerve showed maximum CSA. White arrow indicates the nerve on US image.

Fig. 4 Ultrasonography images of follow-up (0 – 24 months) of cross-sectional area (CSA in mm2) of UN, MN, LP and PT nerves of leprosy patient without reaction (C) in comparison to healthy subject (HS) at 0 months. White arrow indicates the nerve on US image.

Increased neural blood flow (EF) during follow-up

Endo- or perineural flow suggestive of increased neural vascularity by CD imaging in the group with reactions was observed in 20 patients at baseline (49 nerves); in 14 patients in the 3^rd month (17 nerves); 10 patients in the 6^th month (12 nerves); 9 patients in the 12^th month (11 nerves); 7 patients in the 18^th month (8 nerves); and in 1 patient in the 24^th month (1 nerve) ([Table 3]).

Table 3 Presence of endoneural blood flow (EF) observed using color Doppler (CD) during follow-up (0 – 24 months) in leprosy with reactions (R). The decrease in EF in the patients is shown in parenthesis as a percentage.

leprosy reaction (R = 36)		nerves tested for EF
time (in months)	no. of patients (%)	UN	MN	LP	PT	total nerves
0	20 (55.5)	30	11	4	4	49
3	14 (38.8)	14	2	–	1	17
6	10 (27.7)	9	1	–	2	12
12	9 (25)	12	–	2	1	15
18	7 (19.4)	7	–	–	1	8
24	1 (2.7)	1	–	–	–	1

The number of patients with increased neural flow decreased during the follow-up from 20 (out of 36) (55.5 %) at baseline of the study to 1 patient (2.7 %) in the 24^th month.

In the leprosy group without reactions, only 2 patients showed EF during follow-up: 1 patient showed EF in 2 nerves in the 3^rd month. Based on this observation, a private physician questioned whether there was an early reaction and initiated a course of corticosteroids which resulted in a complete reduction in endoneural blood flow in the 6^th month. However, this patient defaulted on treatment, developed pulmonary tuberculosis and EF was again detected in the 12^th month. Another patient without reactions showed EF in the 6^th month. In this patient the question of an early reaction also arose and it was decided to give a course of steroid treatment with a complete reduction of flow.

Discussion

This prospective study demonstrates the ability to monitor disease progression and detect peripheral nerve damage in patients with leprosy using HRUS. This is the first prospective study assessing this in patients with a polyneuropathy. Leprosy patients had clinical and subclinical (sometimes massive) enlargement of the nerves, the ulnar nerve being most commonly involved. In patients with leprosy reactions, the nerves show greater thickening (especially the arm nerves) than in patients without reactions. During follow-up with treatment of leprosy according to the WHO protocol, the size of the involved nerves decreased and the increased neural blood flow, which was present in 20 patients, also diminished during treatment of reactions.

Damage to peripheral nerves is the main consequence of leprosy and may cause deformities and disabilities in patients. Although the number of new cases reported worldwide has dropped from 228 474 in 2010 to 215 656 in 2013, there has been no change in grade 2 deformity levels. Furthermore, the Southeast Asia region, which is responsible for over 70 % of the world’s case load, has shown an increase in both the number and the percentage of grade 2 deformities, indicating that nerve damage continues to be an important challenge in leprosy [3]. Nerve damage can occur before, during and after MDT and is a result of inflammation in the nerves due to immunological reactions. Reactions and neuritis in the nerve are known to be associated with hemodynamic changes in both the epineurium and the perineurium of the nerve fascicles. These changes were formally studied using invasive biopsy techniques in which a sliver of suspicious nerves was biopsied and studied histologically. Corticosteroids are used to treat nerve function impairment. However, the optimal dose and duration of steroid treatment have yet to be established [12]. The findings of our study may help to assess the duration of this treatment for the individual patient until the increased vascularity has disappeared and the nerve size has decreased. It is also helpful to assess whether there is an exacerbation, but more sonographic studies in relation to clinical examinations and additional lab studies indicating a change in immune responses are needed. It is possible that sonography can be used as a surrogate biomarker to assess the effects of new immune-modulating therapies in leprosy patients with reactions. Increased intraneural vascularization detected by ultrasonography in peripheral nerves has not yet been studied extensively in pathological conditions. Just a few authors have reported on increased nerve vascularization using HRUS and CD in median and ulnar nerve entrapment, in chronic inflammatory neuropathy and in leprosy [5] [13] [14] [15]. In healthy subjects, the detection of increased vascularization by CD or power Doppler imaging is rare.

In recent times due to the high risk of acquiring HIV, hepatitis B and HCV, there is a desire to reduce the number of invasive investigations such as slit skin smears and skin and nerve biopsies in the diagnosis of leprosy and many clinicians, dermatologists and leprologists have been looking for alternative tools to diagnose and monitor leprosy [16]. Clinical assessment (palpation of enlarged nerves) and nerve conduction studies are the two most common noninvasive techniques being used by clinicians [17]. Clinical assessment has its limitations because clinical nerve enlargement can be a late sign and the assessment of neuritis can be difficult.

Recently, more sensitive methods have been introduced to detect early neuropathy. Nerve conduction studies and warm detection threshold tests are effective methods for finding early and subclinical nerve damage [12]. Assessment of early changes by nerve conduction studies such as abnormal sensory nerve action potentials (SNAPs) requires good clinical neurophysiological skill. This can be difficult in patients walking barefoot (difficult to obtain SNAP at the feet) and because it is painful it is not an ideal tool for prospective studies [12]. Moreover, it does not provide spatial information about nerve anatomy and surroundings. Similarly, warm detection threshold tests will not be easily applied in the daily care of leprosy patients since the instruments needed to conduct these studies are expensive and the conditions under which the assessments have to take place, a steady environmental temperature of 20 – 25 °C, are difficult to realize in tropical climates [18].

Based on this study and with the knowledge that portable sonography machines are available and HRUS can be learned relatively easily, HRUS could be an ideal tool to monitor changes in the size and blood flow of nerves which are indicators of nerve activity in reactions and can be used to assess response to corticosteroid treatment. Even though there can be some variability in the measurements of US parameters, this technique has high intraobserver reliability [19]. Therefore, HRUS can be used to monitor disease activity in leprosy including reactions and reactivation of disease. This technique may be helpful to detect early subclinical nerve enlargement, changes in nerve morphology and increased nerve vascularization which could lead to early detection of leprosy reactions. Currently, the spatial resolution of CD imaging is not high enough to visualize epineural or endoneural blood flow under physiologic conditions. However, it is able to detect increased endoneural or epineural blood flow. Pathologic conditions may give rise to impaired blood supply due to local inflammation, which increases blood flow that is detectable with color Doppler [20]. The presence of endoneural blood flow in the absence of clinical evidence of nerve involvement in a few patients is a key observation. These patients showed improvement with prednisolone treatment, thus suggesting that it was a subclinical reaction in the nerve detected by US. More research is needed, perhaps a randomized trial to see whether HRUS can usefully predict early neuritis and lead to better treatment outcomes.

Peripheral nerve ultrasonography provides information on the exact location of nerve enlargement and morphological alterations in the nerve including echotexture, fascicular pattern and vascularity. In conclusion, this study establishes the value of HRUS for studying response to corticosteroid therapy by assessing reduction in size (CSA) and EF during follow-up of patients with reactions. This information brings a new dimension to the screening of nerve damage and response to treatment during follow-up of patients with leprosy.

Contributors

MC, LV, SS, SJ contributed to the writing of the paper and analysis of the results. MC, BD, RR, SJ were involved in patient intake and the performing of HRUS and CD imaging. LS was involved in the analysis of the paper. RE was involved in the statistical analysis. All of the authors were involved in the compiling of the report and approved the final version.

Funding

ECD grant from Indian Council of Medical Research. Department of Biotechnology funded Research Associate fellowship. 

No conflict of interest has been declared by the author(s).

Acknowledgments

We thank Dr AK Meena & Dr Muralidhar Reddy Yerasu, Consultant Neurologists (Nizam’s Institute of Medical Sciences, Hyderabad) and Dr J Subbanna (LEPRA Society-Blue Peter Public Health Research Centre, Hyderabad) for referring some of the patients for the study.

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