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Leprosy is a mycobacterial nerve and skin infection, which can be eradicated by antibiotics. Some patients affected by leprosy, once cured, have residual nerve impairment with paralysis and sensory neuropathy. A series of patients with facial nerve paralysis, investigated using clinical, histological and electrophysiological techniques, demonstrated that the nerve pathology was distal to the section of main trunk prior to its bifurcation. Facial reanimation was achieved with a free gracilis-muscle transfer, coapting its motor nerve to the ipsilateral facial nerve trunk proximal to the site of the leprosy pathology, with a moderate clinical result.
It is a mycobacterial infection (M. leprae) of the peripheral nervous system. The invading organism gains access to the peripheral nerve and, through an inflammatory process, causes a peripheral neuropathy.
It is not clear how the bacterium enters the nerve, but it is thought to be by either haematogenous spread from a respiratory infection or direct spread from the subdermal nerve plexus following a skin abrasion. The systemic extent of the disease largely depends on the patient's immune response.
Leprosy may present in several ways, with the consistent features of: (1) diminished sensibility in a typical macule or plaque in the skin; (2) palpable enlargement of one or more peripheral nerve trunks at specific sites, associated with sensory, motor or autonomic impairment in the distribution of the nerve; and (3) the presence of acid-fast mycobacteria in a slit skin smear.
The ‘sites of predilection’ for nerve enlargement are the ulnar nerve at the elbow, the median nerve at the wrist, the lateral popliteal nerve at the fibula head, the posterior tibial nerve at the ankle and exposed superficial cutaneous sensory nerves.
The pathology is thought to occur at these sites for two reasons: first, a superficial nerve is cooler, which is known to be beneficial to M. leprae growth;
and second, the nerve travels beneath an osseoligamentous tunnel at all of these anatomical sites, leading to compression neuropathy of an oedematous nerve trunk. For years it was believed that the nerves were involved exclusively at these sites, but increasingly there is evidence that nerves are involved more proximally and distally to these sites. The proximal level could be treated by neurolysis, whilst distal involvement is often irreversible.
Lesions of the facial nerve differ from other nerve lesions in leprosy because the facial nerve is a pure motor nerve. It was, therefore, chosen as the best model for investigating functional reinnervation of free muscle grafts to treat irreversible muscle paralysis.
In order to use the ipsilateral facial nerve safely to power a free muscle flap, it is essential to be sure that the nerve is physiologically normal at any proposed site of coaptation. A series of clinical studies were carried out to try to delineate the most proximal site of leprous pathology in the facial nerve. Once this anatomical site was known to be free of disease then a free muscle graft could theoretically be reinnervated by donor-nerve coaptation at this point. Many studies that aim to discover the proximal extent of nerve involvement in leprosy have been published elsewhere, and they are summarised in the methods section. A case report of the first free muscle flap in leprosy is then described.
1. Previous studies to delineate the extent of leprous neuropathology in the facial nerve
Complete facial nerve palsy is extremely rare in leprosy, and it is not known how far proximally the pathology extends along the facial nerve. Central nervous system involvement has not been described, so the stapedial reflex was used as a topographical marker to test for intratemporal involvement of the facial nerve by leprosy neuropathology. Leprosy patients with and without facial nerve involvement and non-leprous controls had their ears clinically examined, and underwent a tympanogram and an audiogram (to exclude conductive and sensorineural deafness), followed by measurement of a stapedial reflex and acoustic reflex threshold.
Results showed no differences in the number of absent reflexes and no differences in reflex thresholds between the subjects. The study suggested that facial nerve pathology does not extend proximal to the stylomastoid foramen, unless such proximal involvement is subclinical to the detection methods used.
The next attempt to define the proximal extent of the lesion was by electron microscopy of facial nerve biopsies. Sections of resin-embedded whole extracranial facial nerves and their branches were studied from three patients with leprous irreversible total facial nerve palsy who were undergoing static sling reconstruction.
No consistent pattern of nerve-fibre damage was found. In one case, the temporozygomatic branch was affected but the cervical branch was normal, suggesting that damage begins distally. In two cases, similar losses of nerve fibres in the trunk and in all branches were likely to emanate from damage at a more proximal site. The possibility of proximal compression as a contributory factor in these neuropathies cannot be discounted, particularly when the nerves are swollen. The presence of increased numbers of unmyelinated axons in the motor nerves, often in regeneration clusters in the proximal sections, was evidence of regeneration. These axons probably have the potential to develop into functional myelinated fibres, provided that a viable distal target, e.g. a muscle flap, can be supplied. This study supported a more proximal level of nerve involvement, and suggested that the mechanism of mis-reinnervation is either regenerating axons being misdirected at the level of the main trunk bifurcation or collateral sprouting from non-involved axons into adjacent empty myelin sheaths.
To examine facial nerve function physiologically in less severely palsied patients, an electrophysiological measurement was devised. As the portion of extracranial nerve from the stylomastoid foramen to its bifurcation and clinical disease is only about 2–3 cm long, and because the patients have facial muscle atrophy precluding the use of electromyography (EMG), a centrally evoked action potential had to be collected from the facial nerve proximally. Transcranially evoked compound motor action potentials were collected directly from the surgically exposed facial nerve during a superficial parotidectomy. Nine patients were tested electrophysiologically in the study, before having a neurolysis to treat their partial palsy.
The study showed that the main trunk was always involved by a lesion, and further scattered skip lesions were distributed distally throughout the facial nerve branches. A macroscopically normal facial nerve trunk with reduced conductivity of transcranially stimulated compound nerve action potentials is, in fact, involved with leprous inflammation and fibrosis. The temporozygomatic branches' peripheral involvement was heavier than in other branches. Epineural fibrosis, assessed by a histopathologist, was worse at the sites of skip lesions distally, and gradually became less severe towards the trunk.
These studies suggested that, in severe complete facial nerve paralysis, the proximal facial nerve trunk just distal to the stylomastoid foramen is biologically alive,
It is, therefore, reasonable to expect a new muscle with its motor nerve coapted to this proximal facial nerve trunk to be reinnervated with axons that will subsequently myelinate and produce a muscle contraction in the transplanted muscle. Free muscle transfer with direct facial nerve coaptation could be offered to patients requesting a dynamic reconstruction.
2. Case report
A 39-year-old male had a history of treated borderline tuberculoid leprosy 15 years ago and residual right facial paresis.
2.1 Preoperative assessment
Facial examination revealed an 8 mm lid gap on gentle closure of the right eye, which improved to 2 mm on tight closure, with a good Bell's phenomenon. Eye examination showed no superficial punctate keratosis (SPK) or corneal ulceration, but a slightly wide palpebral fissure. The left facial muscles were normal in tone and power. On the right, there was a weak orbicularis occuli and a mildly weak frontalis muscle, but profound palsy of the buccal musculature and an inability to elevate or laterally deviate the right commissure of the mouth. He had normal platysma and depressor anguli oris function. This was interpreted as a partial palsy of the temporozygomatic branches, a total buccal plexus palsy with some residual mandibular-branch function and full cervical-branch function (Fig. 1) . There was no cutaneous sensation in the middle third of the right side of his face. An ENT examination confirmed normal right tympanic membrane, tympanogram, audiogram and stapedial reflex. He complained of epiphora when out in cold weather and whilst eating (crocodile tears or Bogorad's syndrome).
Figure 1Preoperative view demonstrating right facial nerve palsy. Note the lagophthalmos, loss of nasolabial fold on the right, marked facial asymmetry on smiling and wasted hollow in the right cheek.
Electromyography with surface electrodes confirmed voluntary muscle contraction of the frontalis and platysma. An absent electromyogram from the lower eyelid and levator labii superioris whilst attempting to smile substantiated the clinical palsy. A bipolar concentric needle electrode electromyogram showed considerable baseline artefact but no voluntary contraction or fibrillation potentials in the right upper lip.
2.3 Operative procedure
Surgery consisted of a medial tarsorrhaphy for the right eye. Through a facelift incision, a right superficial parotidectomy exposed the right facial nerve. The main trunk looked healthy under the operating microscope, with a soft white normal-diameter nerve. The facial trunk branches were type II as described by Katz and Catalano,
which made it easy to preserve the zygomaticotemporal, mandibular and cervical branches, using the central three branches, which came from a common trunk, as the proximal nerve stump for the gracilis nerve coaptation. Part of the right gracilis muscle (two-thirds of the width and 11 cm long) was harvested with an 8 cm anterior obturator nerve and a 6 cm vascular pedicle. The dissected gracilis portion was refashioned using its own epimysium. The muscle was fixed to the malar periosteum cephalad, and divided distally and sutured into the upper and lower lips. Revascularisation was achieved by anastomosis with the facial vessels, and the nerve was coapted at the level of the bifurcation of the facial nerve trunk. The patient made a good recovery, apart from a small salivary fistula, which spontaneously closed by the 19th postoperative day. The patient was noted to have a symmetrical mouth at rest.
Histological examination of the proximal facial nerve biopsy revealed three fascicles from one trunk all containing moderate numbers of myelinated fibres and regenerating clusters. There was no evidence of increased endoneural collagen, no inflammatory cells and no bacilli.
2.4 Clinical result
At follow-up 7 months postoperatively there was visible evidence of the free gracilis muscle bulk (Fig. 2) . At 14 months postoperatively there was unequivocal muscle contraction when he tried to smile, but it was not large enough to move the commissure laterally. An electromyogram carried out by an independent neurologist confirmed the viability of the muscle graft and its reinnervation. On review 4 years postoperatively there was no spontaneous facial grimace on attempted smile, or any other facial expression. The gracilis muscle tone maintains the static position of the modiolus, but with no independent movements other than a slight flicker of muscle contraction (Fig. 3) .
Figure 2Appearance 7 months postoperatively, showing the small medial tarsorrhaphy, a fullness in the right cheek from the gracilis muscle transplant and the static positioning of the right modiolus.
Figure 3Appearance 4 years postoperatively, (A) at rest and (B) attempting to smile, demonstrating the maintained static position of the commissure and some functional grimace from a reinnervated gracilis muscle.
The pattern of facial-nerve involvement in leprosy is predominantly a zygomatic branch palsy causing lagophthalmos. Dastur et al compared facial nerve involvement with trigeminal nerve malar skin patches.
They suggested that retrograde motor branch infection with leprous bacilli was followed by facial palsy. From a facial skin patch, the bacteria gain access to the maxillary branch of the trigeminal nerve and, through interconnections with the facial nerve (purely motor), the latter becomes involved. This observation has been confirmed by others.
The significance of facial patches and type I reaction for the development of facial nerve damage in leprosy: a retrospective study among 1226 paucibacillary leprosy patients.
Figure 4A new patient with a leprous facial patch in reversal reaction. He later developed a facial nerve palsy, which completely recovered after a course of corticosteroids.
Leprosy patients with an irreversible facial nerve lesion (defined as more than 3 years facial palsy, with no improvement after corticosteroids) have little hope of functional or even cosmetic reconstruction in the developing world. The options for management are primarily directed towards preventing blindness from corneal exposure and treating oral incontinence.
The lagophthalmos is treated by health education, ‘think–blink’ exercises
which is more aesthetically pleasing than a lateral or medial tarsorrhaphy. Those with a lid gap of more than 8 mm are offered a Johnson dynamic reconstruction
using the posterior third of the ipsilateral temporalis muscle lengthened by a strip of fascia lata. I prefer this reconstruction to the classic Gillies technique,
as the direction of the fibre pull is more physiological and the cosmesis is superior.
Severe oral incontinence can be managed by a static fascial sling suspended from the malar to control the drooping mouth. A dynamic reconstruction is possible using a portion of the temporalis muscle.
However, use of the temporalis muscle for severe lagophthalmos precludes its use for dynamic facial reconstruction. Other options for a functional muscle transfer would be the masseter,
in: Georgiade G.S Georgiade N.G Riefkohl R Bavick W.J Textbook of Plastic, Maxillofacial and Reconstructive Surgery. Williams and Wilkins,
Atlanta1992: 581-595
For these to be truly functional (rather than just dynamic), they would need an interpositional nerve graft from the ipsilateral facial nerve. Such a reconstruction would avoid a free flap and thus be a more appropriate technique for the developing world. The possibility of neurotising one of these local muscles (masseter, sternocleidomastoid, digastric or trapezius) from the proximal facial nerve was tested in cadavers in order to avoid a vascular anastomosis. I considered the temporalis muscle as a possible donor as its innervation is free from leprous infection. A postmortem dissection of the temporalis muscle from a cephalad direction, denervating it but leaving its two vascular pedicles (type III muscle)
intact, showed that a nerve graft would be necessary to reach from the facial nerve trunk to the temporalis' two motor nerves. There was also the possibility of spontaneous reinnervation from the muscle's own nerve unless it was carefully directed away from the new coaptation. A true neurotisation to the temporalis muscle with a nerve graft from the facial nerve, as was sometimes used before free muscle transfers were developed,
would also be possible but would again need a nerve graft. However, all these techniques require a donor nerve graft. Finding a donor nerve is not easy in leprosy as any superficial cutaneous nerve normally used in reconstruction (e.g. sural nerve, medial cutaneous nerve of the forearm or an intercostal nerve) is likely to be involved. I studied sensory loss in the lower abdomen and groin area in 10 male patients, to see whether this relatively warmer area would yield non-involved superficial nerves, but approximately half of these men had some sensory deficit in their groin skin. Even if this is only dermal sensory nerve ending loss, it remains risky to try to use a donor nerve from this area.
A cross-facial interpositional nerve graft from the non-involved side is risky, as 50% of leprous facial nerve palsies are bilateral
and those that are not often have a subclinical facial nerve lesion, as evidenced by the frequent finding of mis-reinnervation on the contralateral non-palsied side (personal observation). Mis-reinnervation (synkinesis) is the observation of involuntary co-contractions of physiologically unrelated voluntary muscles of facial expression during blinking, talking, smiling, etc.
The spinal accessory nerve, which innervates the sternocleidomastoid and trapezius muscles, is also of interest. It is a relatively superficial nerve in the neck, yet the trapezius muscle has not been reported to be paralysed in leprosy. This may be because no one has looked for this, rather than because it does not occur. The 11th cranial nerve usually pierces the superior third of the sternocleidomastoid muscle and gives off a small innervating branch; I considered this as a non-free-flap option to avoid having to denervate the trapezius muscle. Dissection of a fresh cadaver showed that the dissected sternocleidomastoid branch of the spinal accessory nerve would reach the proximal facial nerve trunk, but the occipital vasculature would need interpositional vein grafts to allow the muscle to sit comfortably in the face. Ryan found the same to be true when using a trapezius muscle for facial reanimation.
Technical issues relating to the choice of the donor muscle have centred on the donor deficit and its functional anatomy. Muscles used in the past include the gracilis, latissimus dorsi, serratus anterior, pectoralis minor, extensor digitorum brevis and rectus abdominis. Freilinger and Frey argue that the specific muscle used is not as important as its placement in the face and its functional anatomy.
A short muscle with a functional length of 4–7 cm, a contractile capability of 1–1.5 cm and sufficient strength to move the facial soft tissues effectively is required. A constant vascular pedicle and nerve supply facilitate reliable microvascular transfer. Experience has shown the gracilis muscle to be technically easy to harvest, and a custom-made portion of the muscle can be used with minimal donor-site morbidity, although others use the pectoralis minor, especially in children.
Different muscles have different ratios of nerve axons to muscle fibres. Normal facial muscle and platysma have about 25 muscle fibres innervated by one axon;
The gracilis and pectoralis minor are seen as ‘stupid’ muscles, as they have between 1500 and 2000 muscle fibres per axon. The extensor digitorum brevis, like other distal-limb small muscles for fine movement, has 200–300 muscle fibres per axon and is neither ‘stupid’ nor ‘intelligent’. Muscles with large numbers of motor units, with few muscle fibres per unit, can achieve fine movements, whilst the proximal-limb muscles are more concerned with powerful gross movements. There are some theoretical advantages to using a ‘stupid’ muscle for facial reanimation, as the success of nerve growth into the muscle transplant is less than 50%, and the more muscle fibres each axon can control, the greater the chance of a functional result. Loss of this fine innervated control probably accounts for the loss of spontaneous smiles in these patients.
The gracilis muscle was chosen because of its ease of dissection, plasticity to the defect and low donor-site morbidity. It also has the long vascular and nerve pedicles that are essential for this type of reconstruction. The ipsilateral facial nerve trunk is about 11 cm from the facial vessels necessary for vascular anastomosis.
However, the importance of this study is not so much the successful treatment of a few leprosy patients with facial palsy but the potential for sensory recovery in much larger numbers of patients. The complications of complete sensory loss in the feet and hands are often disastrous, leading to toe, foot or leg amputations, and digit and functional loss in the upper limb, respectively, compounded not infrequently by social ostracism. If we could replace a portion of heel or hand skin with a new skin envelope containing non-leprosy-involved sensory organs and reinnervate that free flap with the patient's own peripheral nerve, then protective sensation, the single most useful function to the leprosy sufferer, would be restored. The peripheral nerve trunk in leprosy is involved considerably more proximally than is seen by the naked eye.
Intraoperative electroneurodiagnostics to detect a second granuloma in the cubital area of the median nerves affected by leprosy: a new approach to prevent incomplete surgery.
A local (i.e. hand or heel) vascular anastomosis will be feasible, but the donor nerve will need to be considerably longer, maybe as long as 35 cm for the median, 50 cm for the ulnar or 70 cm for the posterior tibial nerve. Such long donor nerves do not yet exist, but prefabrication with expanded polytetrafluoroethylene (Gore-Tex) or similar tubes, together with growth and neurotrophic hormones may be able to create ‘designer’ flaps.
This is the first time that a functional muscle transfer has been used in a person affected by leprosy. The patient has clinical evidence of a surviving and reinnervated gracilis muscle. Free muscle transfer for facial palsy in persons affected by leprosy is technically possible, so long as the donor muscle and nerve are not diseased and the nerve coaptation is proximal to the facial nerve bifurcation. Sensory recovery in leprosy neuropathy is now a possibility, but will need to wait for the new technologies of very long alloplastic nerve conduits.
References
Antia N.H
Shetty V.P
The peripheral nerve in leprosy and other neuropathies. Oxford University Press,
Delhi1997
The significance of facial patches and type I reaction for the development of facial nerve damage in leprosy: a retrospective study among 1226 paucibacillary leprosy patients.
in: Georgiade G.S Georgiade N.G Riefkohl R Bavick W.J Textbook of Plastic, Maxillofacial and Reconstructive Surgery. Williams and Wilkins,
Atlanta1992: 581-595
Intraoperative electroneurodiagnostics to detect a second granuloma in the cubital area of the median nerves affected by leprosy: a new approach to prevent incomplete surgery.
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