Asymmetrical Brachial Plexus Involvement with Greater Auricular Nerve Involvement in Borderline Tuberculoid Leprosy: An Electrophysiological and Radiological Correlation

Abstract

Leprosy, caused by Mycobacterium leprae, is known for mainly affecting the peripheral nerves. But in recent years, there is growing recognition that it can also involve the central nervous system, including the spinal cord and the brachial plexus. This broader understanding of nerve involvement highlights the importance of newer diagnostic tools like nerve conduction studies, high-resolution ultrasonography, and magnetic resonance imaging, which can help detect and assess these deeper structures and more complex manifestations. We present an intriguing case of a 27-year-old male diagnosed with borderline tuberculoid leprosy based on histopathology, who was found to have brachial plexopathy on nerve conduction studies and magnetic resonance imaging, along with involvement of the greater auricular nerve as revealed by high-resolution ultrasonography.

 

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Keywords

asymmetrical brachial plexopathy - greater auricular nerve - high-resolution ultrasound - magnetic resonance imaging - nerve conduction study

Introduction

Leprosy is a chronic and debilitating infectious disease caused by Mycobacterium leprae. It mainly affects the peripheral nerves, skin, mucosa of the upper respiratory tract, eyes, and the reticuloendothelial system. Emerging studies and case reports have increasingly suggested that the central nervous system, including the spinal cord and brachial plexus, may also be involved in leprous neuropathy.[1] [2] [3] Magnetic resonance imaging (MRI) is commonly used to evaluate the brachial plexus, brain, and spinal cord. The imaging characteristics can differ, showing bilateral or unilateral involvement, which may be symmetric or asymmetric, and can include smooth or irregular thickening of the divisions and cords. Alongside MRI, nerve conduction studies (NCS) are conducted to assess the functional status of nerves, which provide insights into nerve conduction velocity, amplitude, and latency, aiding in distinguishing between axonal damage, demyelination, and a mixed pattern of both.[4] This case report highlights the involvement of both the brachial plexus and the greater auricular nerve in a patient with leprosy, emphasizing the importance of MRI and NCS in the early diagnosis of brachial plexopathy with peripheral nerve involvement.

 

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Case Report

A 25-year-old man presented to our dermatology outpatient department with a chief complaint of a reddish plaque over the left side of his face, extending from the forehead down through the orbital and zygomatic regions, along with erythema over the left ear. He also reported a 7-month history of pain in the right shoulder radiating down the arm and forearm, difficulty moving over the right shoulder, accompanied by paresthesia, numbness, and sensory loss in the right ulnar distribution of the hand on the palmar and dorsal surface of the hand for the past 6 months. Over the last 4 months, he experienced a noticeable weakness in his right-hand grip. Dermatological evaluation revealed a solitary, well-defined erythematous plaque measuring approximately 4 × 7 cm on the left side of the forehead, extending to the zygomatic area, associated with reduced temperature sensation ([Fig. 1A], black arrows). Erythema of the left ear was also noted ([Fig. 1A], red arrows). On physical examination, the right ulnar nerve was significantly thickened at the level of the medial epicondyle, and tenderness was noted over the median nerve at the wrist. The left greater auricular nerve was visibly prominent and palpable ([Fig. 1A], green arrows). Sensory examination showed a near-complete loss of touch, pain, and temperature sensations over the right ulnar distribution involving palmar and dorsal surface of hand, extending proximally to the mid-forearm. Sensory examination over plaque which was present on the face revealed normal sensations. Motor assessment revealed impaired abduction and adduction of the little finger with difficult raising of his right arm. Slit skin smears from the earlobes were negative for acid–fast bacilli. Histopathological examination of a skin biopsy from the plaque demonstrated epithelioid cell granulomas with Langhans giant cells in the dermis, without caseous necrosis ([Fig. 2]). Given the neurological findings, NCS was performed, which revealed right brachial pan-plexopathy. Motor potentials were non-recordable from the right median nerve, with reduced amplitude in the right ulnar nerve. Sensory potentials were absent in the right ulnar, right lateral, medial antebrachial cutaneous nerves, and right radial nerve ([Figs. 3] and [4]). These significant abnormalities on NCS warranted further evaluation. MRI of the brachial plexus and high-resolution ultrasonography (HRUS) of the greater auricular nerve and ulnar nerve were subsequently performed to assess the extent of neural involvement. HRUS with a linear probe at 12 MHz transducer revealed increased cross-sectional area of left greater auricular nerve (CSA- 3 mm²; [Fig. 5], [Video 1], demonstrating the same) and of right ulnar nerve (12 mm²; [Fig. 6]). MRI (1.5 T GE MRI Machine) was performed subsequently to evaluate the proximal extent of nerve involvement using routine MR sequences including axial T1, axial T2, axial and coronal proton density fat saturated, and in addition using coronal and sagittal 3D short-tau inversion recovery sequence, 3D diffusion-weighted imaging/apparent diffusion coefficient, axial T1 FS pre- and postcontrast sequences. MRI revealed smooth thickening, involving the entire right brachial plexus extending from its roots to branches ([Fig. 7A, C]), more marked hyperintensity at the right C8–T1 nerve, and asymmetrical hyperintensities seen in bilateral brachial plexus ([Fig. 7B]).

Video 1 Video demonstrating the course of left greater auricular nerve on HRUS with a linear probe at 12Hz transducer which revealed increased cross-sectional area of the nerve.

Fig. 1 (A) Well-defined erythematous plaque measuring approximately 4 × 7 cm on the left side of the forehead, extending to the zygomatic area (black arrows). Erythema of the left ear was also noted (red arrows) Green arrows depict the prominence of left greater auricular nerve on examination. (B) Patient was followed up at 6th week, and there was a resolution in the erythema of the plaque and decreased visibility of the greater auricular nerve (green arrows).

Fig. 2 Histopathological examination of a skin biopsy from the plaque demonstrated epithelioid cell granulomas (red arrows) with multinucleated Langhans giant cells in the dermis (black arrows) without caseous necrosis.

Fig. 3 Here is the normal nerve conduction study waveform of a healthy person (A) taken for comparison with the nerve conduction study report of our patient (B). In figure B, Sensory waveforms in NCS revealed that sensory potentials were absent even on high voltages in the right ulnar (black encircled) and right median nerve (yellow encircled) as compared to normal NCS (A).

Fig. 4 Here is the normal nerve conduction study waveform of a healthy person (A) taken for comparison with the nerve conduction study report of our patient (B). In figure B, Sensory waveforms in NCS revealed that sensory potentials were absent even on high voltages in the right lateral (green encircled) and medial antebrachial cutaneous nerve (sky blue encircled) compared to normal NCS (A).

Fig. 5 (A) HRUS revealed increased cross-sectional area of greater auricular nerve (3 mm²) on the transverse axis. (B) The longitudinal axis of the nerve is demonstrated by a white dotted line, which revealed the thickness of the epineurium. (Greater auricular nerve runs superficial to the sternocleidomastoid muscle [SCM], which was used as a landmark.)

Fig. 6 Increased cross-sectional area (CSA) of the right ulnar nerve demonstrated on longitudinal axis (A) and transverse section (B). On the transverse axis, CSA was 12 mm² and the nerve was hypoechoic. (Medial epicondyle [ME] was taken as a bony landmark for the ulnar nerve.)

Fig. 7 (A) Coronal post contrast fat sat image on MRI shows smooth thickening involving the entire right brachial plexus extending from its roots to branches (yellow arrows). (B) Coronal 3D STIR images showing asymmetrical hyperintensity in the bilateral brachial plexus, with more on the right upper limb (yellow arrow) as compared to the left upper limb (red arrow), more marked T2/STIR hyperintense thickening noted in the right ulnar nerve, more marked in the ulnar groove (green arrow). (C) MRI revealed smooth thickening involving the entire right brachial plexus extending from its roots to branches (lateral view; black arrows).

Based on the clinical, histopathological, electrophysiological, and radiological findings, a diagnosis of borderline tuberculoid leprosy with greater auricular nerve involvement and asymmetrical brachial plexopathy of the right hand was made. Patient was started on WHO multibacillary multidrug therapy (MB-MDT), constituting rifampin (600 mg/month), clofazimine (300 mg/month and 50 mg daily), and dapsone (100 mg daily) for 12 months, and a tapering dose of prednisolone 0.5 mg/kg for management of brachial plexopathy. The patient was advised to undergo supportive and rehabilitative physiotherapy. Patient was followed up at 6th week and there was a resolution in the erythema of plaque ([Fig. 1B]). There was improvement of sensory symptoms without tenderness and decreased visibility of the greater auricular nerve ([Fig. 1B], green arrows). Follow-up NCV showed improvement in the sensory potentials of the right ulnar nerve. Due to financial difficulties, follow-up MRI sequencing was not done.

 

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Discussion

This case report highlights the significance of combining electrophysiological and radiological tools in the diagnosis of brachial plexopathy in a patient with borderline tuberculoid leprosy. While brachial plexus involvement is more frequently seen in the borderline tuberculoid form, it can also manifest across other types within the leprosy spectrum.[5] [6] [7] Some studies have also shown the involvement of central nervous system and spinal cord.[8] In this case, NCS revealed subclinical nerve involvement, as evidenced by abnormalities in the right lateral and medial antebrachial cutaneous nerves, despite the absence of clinical signs—indicating an early or preclinical stage of brachial plexus involvement. Beyond its diagnostic value, NCS also serves as a useful tool for monitoring the response to MDT in leprosy.[9] In our case, the patient presented with clinical signs indicative of Hansen's disease and showed smooth, bilateral asymmetrical thickening of the brachial plexus more pronounced on the right side, appearing as hyperintensities in the trunks and divisions on T2/STIR MRI sequences. These imaging findings align with those documented in larger series and individual case reports, which typically describe smooth or mildly irregular thickening of plexus components, characterized by hyperintensities without nodular formations or notable postcontrast enhancement.[1] [10] As MRI also detected subtle abnormalities in the opposite limb, further emphasizing its crucial role in improving the diagnostic precision of leprosy neuropathy. HRUS has become an important tool for evaluating peripheral nerve involvement. In this case, HRUS was favored over MRI for examining the greater auricular nerve due to its superficial position and the cost-effectiveness of the technique. Moreover, HRUS is helpful in differentiating nerve thickening from other possible conditions, such as a thrombosed external jugular vein, enlarged cervical lymph nodes, or tuberculous cold abscesses. A variety of treatment options exist for brachial plexopathy, including nonsteroidal anti-inflammatory drugs, corticosteroids, tricyclic antidepressants, and membrane-stabilizing medications like carbamazepine and gabapentin.[11]

 

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Conclusion

This case highlights the complementary utility of HRUS, NCS, and MRI in diagnosing multilevel nerve involvement in leprosy. While NCS provided a functional assessment of the nerves, MRI offered detailed anatomical insights. HRUS proved to be a practical, affordable modality for evaluating superficial nerves such as the greater auricular nerve.

 

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Conflict of Interest

None declared.

• References

• 1 Bhoi SK, Naik S, Purkait S. Pure neuritic leprosy with bilateral foot drop and central nervous involvement: a clinical, electrophysiological, and MR correlation. Neurol India 2021; 69 (05) 1349-1353
• 2 Mittal A, Dhanota DPS, Saggar K, Ahluwalia A. Brachial plexopathy with ulnar nerve abscess in leprosy: a case showing importance of magnetic resonance neurography with clinical, imaging and histopathological correlation. Indian J Dermatol Venereol Leprol 2022; 88 (03) 385-388
• 3 Nalini A, Singh RJ, Saini J, Prasad C, Mahadevan A. Magnetic resonance neurography identifies involvement of plexuses in leprous neuropathy. Neurol India 2015; 63 (04) 624-626
• 4 Nisargandha MA, Parwe SD, Lade NR, Padathpeedika Khalid J, Kuchewar VV. Assessing nerve conduction velocity as a diagnostic and prognostic indicator in leprosy patients: a cross-sectional study. Cureus 2024; 16 (04) e58294
• 5 Jabeen S, Saini J, Vengalil S. et al. Neuroimaging in leprosy: the nerves and beyond. Radiol Infect Dis 2020; 7 (01) 12-21
• 6 Polavarapu K, Preethish-Kumar V, Vengalil S. et al. Brain and spinal cord lesions in leprosy: a magnetic resonance imaging–based study. Am J Trop Med Hyg 2019; 100 (04) 921-931
• 7 Elangovan K, Kumar S, Garg RK. et al. Neuroimaging in leprosy: a case series exploring domains beyond peripheral nerves. Cureus 2025; 17 (04) e81571
• 8 Verma S, Garg RK, Rizvi I. et al. Central nervous system, spinal root ganglion and brachial plexus involvement in leprosy: a prospective study. J Cent Nerv Syst Dis 2022; 14: 11 795735221135477
• 9 DeFaria CR, Silva IM. Electromyographic diagnosis of leprosy. Arq Neuropsiquiatr 1990; 48 (04) 403-413
• 10 Poojar M, Singh R, Nalini A. et al. Neurography in Hansen's neuritis (P6. 030). Neurology 2015; 84 (14, Suppl): 6-030
• 11 Ghia D, Gadkari R, Nayak C. Complex regional pain syndrome secondary to leprosy. Pain Med 2012; 13 (08) 1067-1071

Publication History

Article published online:
16 September 2025