Background

Leprosy is a chronic infectious disease caused by an acid-fast rod-shaped bacillus, Mycobacterium leprae. It is an important cause of neuropathy in India, and cranial nerve involvement is seen in 10 to 17.6% patients.1 2 Although the incidence of leprosy is declining, and with the advent of multi-drug therapy lesser complications are now observed, India is still the home of approximately 55% of newly detected patients with leprosy globally.3 Data regarding mis-reinnervation are sparse and roughly one-third patients with facial muscle impairment may show evidence of the same.4 Bilateral occurrence of facial synkinesis, which is an important clinical marker of mis-reinnervation, is rare. We describe a patient of lepromatous leprosy presenting with bilateral and symmetrical facial synkinesis without any history of facial pareses. Electrophysiological details and pathophysiology are also discussed.

Case presentation

A 35–year-old gentleman presented with complaints of numbness involving the right half of his face for 8 months. The decrease in sensations was initially noticed by the patient in the area of the lower jaw and the cheek which subsequently progressed to involve the forehead for the past 2 months. Stretching sensation over the nose was appreciated during blinking from the past one and a half months. There was no history of electric current like sensation, trauma, surgery involving the face or cranium or any chronic ailment. On examination, perception of pain was decreased by more than 50% in the distribution of right trigeminal nerve including all the three divisions. Mild weakness was present in the right temporalis, masseter and pterygoids. Synkinetic movements involving the orbicularis oculi and nasalis, on both sides, were observed during the process of blinking (video 1). A total of seven hypopigmented hypoesthetic patches, approximately 15–25 mm in diameter, spread over the upper limbs and on the back were observed. Right supraorbital nerve and great auricular nerves were enlarged. Examination of the nervous system did not reveal any other abnormality.

Investigations

Electrophysiological evaluation revealed loss of blink reflex on the right side, and low amplitudes on facial motor study of orbicularis oculi, orbicularis oris and nasalis, with normal latencies. No potentials could be recorded from stimulation of the great auricular nerves. Modified blink reflex5 was used in two sets for the assessment of presence of mis-reinnervation. The first set used orbicularis oculi and nasalis while orbicularis oculi and orbicularis oris were used in the second set. The modified blink reflex was feasible only on the left side owing to involvement of trigeminal nerve on the right side; simultaneous responses were observed in the first as well as second set of montage, the first one being more robust in amplitude than the second one (figure 1). Surface electromyography was done but the amplitudes recorded were very low (recording nasalis) during spontaneous blinking. Electrophysiology of the nerves of the limbs was normal. Haemogram and routine biochemical parameters, including blood sugar and glycosylated haemoglobin, were within normal limits. No abnormality was detected on antinuclear antibody test, extractable nuclear antigen profile and angiotensin-converting enzyme level estimation. Biopsy of the hypoesthetic cutaneous lesion over the forearm showed lepra bacilli; sural nerve biopsy was suggestive of granulomatous infiltration of the nerve fibres.

• Download figure
• Open in new tab
• Download powerpoint

Figure 1

Modified blink reflex done on the left side of the patient. (Note: supraorbital nerve on the right side could not be stimulated). (A) First set of montage using orbicularis oculi (upper trace) and nasalis (lower trace) depicts R₁ and R₂ responses with similar latencies in the two recorded muscles. (B) Second set of montage using orbicularis oculi (upper trace) and orbicularis oris (lower trace) depicts delayed latency of R₁ (very low amplitude, arrow) and R₂ responses recorded from the orbicularis oris. The lower trace has been recorded at 50 microvolt per division instead of 100 microvolt per division.

Treatment

With a diagnosis of multi-bacillary leprosy, the patient was initiated on WHO multi-drug therapy with supplemental prednisolone for 6 weeks.

Outcome and follow-up

After 3 months of follow-up, an improvement in facial sensations was observed but without any change in facial synkinetic movements.

Discussion

Leprosy is a chronic infectious disease with an insidious protracted course. Leprous neuropathy, with or without thickening of the nerves, is an important cause of neuropathy with sequelae in the form of damage, sensory obtundation or deformity of the affected part. Cranial nerve involvement in leprosy is seen in 10 to 17.6% patients and facial nerve followed by trigeminal nerve are the ones most commonly affected.1 2 The first documentation of mis-reinnervation affecting the facial nerve in leprous neuritis was done by Ranney et al6 who subsequently described 12 patients of leprosy with bilateral facial palsy and extrapolated the prevalence of mis-reinnervation to be 35%.7

Synkinesis, an abnormal synchronous activity of muscles that normally do not contract together, with voluntary and reflex movements, is an important clinical marker of mis-reinnervation. It signifies cross-connections associated with regeneration of a nerve secondary to an injury, such as Bell’s palsy, surgical or non-surgical trauma, infection, etc., in varied proportions. Evidence of denervation after an axonal injury is usually seen within 3 weeks of the insult while that of reinnervation may not appear until 3 months into the process of regeneration of the nerve.5 The first step in regeneration is the appearance of axon cones from the proximal part of the nerve stumps which then grows distally. Bands of Bungner serve as a guide to direct the developing funiculi of the respective motoneurons to the appropriate muscle. Reinnervation proceeds normally (attainment of preinjury status) if factors like non-viable bands of Bungner, fibrosis or scarring of the local tissue, or atrophied target tissue do not impede the process; however, abnormalities may occur owing to the aforementioned factors leading to mis-reinnervation.8 These mis-reinnervation patterns may occur in terms of abnormal nerve-branching affecting one single muscle or abnormal target-innervation affecting more than one muscle. Abnormal target-innervation is the basic pathophysiological error involved in the development of synkinesis (figure 2). In addition to these mis-reinnervation patterns, associated phenomena of lacrimation and sweating may be seen due to involvement of the secretomotor fibres.

• Download figure
• Open in new tab
• Download powerpoint

Figure 2

Flowchart showing pathophysiology of synkinesis in nerve injury.*Oriented columns of laminin-1 and aligned Schwann cells (appearing as bands of spindle-shaped cells) in the denervated zone.

Our patient had evidence of involvement of the zygomatic (orbicularis oculi) as well as the buccal branch (nasalis, orbicularis oris) of the facial nerve. Nasalis has not been shown to be involved either in cases on surgical exploration or as a constituent of mis-reinnervation after leprous neuropathy.4 9 The predilection for involvement in leprous facial neuropathy has classically been stated for the peripheral zygomatic branches in concordance with the preference for relatively cooler parts of the body.10 This concept, however, is not without challenge with documentations stating involvement of the main trunk and a scattered distribution throughout the facial nerve, thereby implying haematogenous spread of the lepra bacilli.4

The minimum duration between the diagnosis of leprosy and onset of cranial nerve symptoms has been reported to be 4 months.2 The total duration in our case was 8 months and one and a half months with respect to involvement of the trigeminal nerve and facial nerve, respectively. Strikingly no suggestion or evidence could be found of obvious facial palsy; this points towards a smouldering subclinical neuritis of the facial nerve in patients with leprosy. An emphatic statement regarding the onset of involvement, simultaneous or rapidly sequential, of facial nerve in our case cannot be made as he had not been examined previously. The synkinetic movements at the time of presentation were fairly symmetrical and asymmetry in power was not detected.

Additional evaluation of nasalis in our case was required owing to its conspicuous involvement with orbicularis oculi. Given the specificity of orbicularis oculi in the blink reflex5 and the ease of analysis involved in the study of nasalis, the recording of propagated potentials through regenerated nerves may be rewarding in the documentation of mis-reinnervation. The delineation of involvement can have important bearing on the subsequent management, especially if selective neurolysis of the nerve branches is being planned.4