Insect bite and arrows

A 68 year old man was noted by his wife to have an “insect bite” on the pinna of his left ear. The lesion was red and swollen like a blister. The patient described shooting pains “like arrows” originating from his left ear and radiating over the top of his head. On the morning of presentation he was unable to close his left eye, and his wife noticed that the left corner of his mouth was drooping. Examination of the ear showed several crusted lesions and blisters in the left external acoustic meatus and pinna (fig 1).

The patient was asked to close his eyes firmly and attempt to smile. Fig 2 shows that he was unable to close his left eye and the left side of his mouth remained motionless. While forcing his right eyelid shut against resistance, the left eye rolled upwards. When asked to raise his eyebrows, the left side remained motionless. Oral examination was normal.

Fig 1 Left external acoustic meatus and pinna

Questions

1. Which sign is shown when the patient's eye rolls upwards?
2. What condition is this patient likely to have?
3. How should this patient be managed?

Answers

1. This is a positive Bell's sign (see discussion).
2. These signs and symptoms are pathognomonic of Ramsay Hunt syndrome. The lesions on the ear are those of herpes zoster and not an insect bite.
3. Without careful examination of the ear, it might have been assumed that this patient was suffering from a Bell's palsy.¹ However, the lesions in the external acoustic meatus and pinna indicate that this patient's facial palsy is caused by the virus herpes varicella zoster. Initial treatment should therefore be with intravenous acyclovir.^{2- 3} Of equal importance is care of the exposed eye, which is at risk of corneal abrasions. The eye should be protected with an eye patch and kept moist with artificial tears.

Discussion

In a series of presentations and papers published from 1907 onwards, James Ramsay Hunt, a consultant neurologist, described in detail the condition now recognised as Ramsay Hunt syndrome. As a former president of the American Neurological Association he presented cases of facial palsy associated with herpetic lesions found specifically in the cutaneous distribution of the facial (VIIth) nerve. Herpetic vesicles and crusting lesions may be found in the external auditory meatus and the area of the pinna immediately surrounding it (zoster oticus), behind the ear on the mastoid process, as well as the anterior two thirds of the tongue and hard and soft palate. The lesions are almost always unilateral and on the same side as the facial palsy.

Ramsay Hunt hypothesised that patients formerly infected with varicella (chickenpox) could have a reactivation of latent virus which had lain dormant in the geniculate ganglion of the facial nerve. The exact pathophysiology remains unclear, but either the direct effect of the virus on the ganglion or the swelling of the ganglion within the intracranial path of the nerve causes paralysis of the muscles it supplies.⁴ Reactivation of the virus is thought to be triggered by stress—for example, a neurosurgical operation, an upper respiratory tract infection, ultraviolet light, or dental extraction.⁵

Ramsay Hunt and colleagues relied on clinical diagnosis of this condition. The diagnosis can now be confirmed by polymerase chain reaction of the virus using swabs taken from the vesicles.⁶ Early diagnosis may also be achieved with contrast magnetic resonance imaging, which shows enhancement in the facial nerve.⁷

Fig 2 Unilateral facial palsy

Anatomical explanation

The distribution of the herpetic lesions is in areas of skin or mucosa whose sensory fibres can be traced back to the geniculate ganglion. Although the anterior two thirds of the tongue receives sensory innervations from the lingual nerve (branch of the trigeminal nerve), it also receives taste fibres from the chorda tympani. The chorda tympani fibres branch away from the facial nerve shortly after the geniculate ganglion and then merge with the lingual nerve before entering the tongue.

The lack of eyebrow movement on the affected side is an important diagnostic sign as it confirms that this is a lower motor neurone lesion. If it were an upper motor neurone lesion, crossover of motor fibres from the ­contralateral side would have retained some degree of movement.

Clinical signs

The most obvious clinical sign associated with Ramsay Hunt syndrome is the facial palsy. With few exceptions it is unilateral, but the severity of the palsy can vary from a weakness to a dense palsy. Idiopathic unilateral facial palsies are generally termed Bell's palsies. Bell noticed that when patients with a dense facial palsy are asked to close their eyes tightly, the eye on the affected side will roll upwards. This is a positive Bell's sign and it was easily shown in this patient. Patients with a facial paralysis due to Ramsay Hunt syndrome are less likely to recover fully than those with Bell's palsy. Facial palsy caused by herpes zoster but without any obvious cutaneous lesions (zoster sine herpete) may lead to a misdiagnosis of Bell's palsy. These patients may not receive antiviral treatment at all, or at least not until herpetic lesions appear, though recent studies suggest benefit from treating all patients with Bell's palsy with acyclovir and steroids.² Delay in initiating treatment may reduce the likelihood of a complete recovery.⁸

Patients describe sensations varying from anaesthesia to painful hyperaesthesia in the distribution of the facial nerve. Bell's palsy is pain free. This neuralgia may not resolve completely and can be extremely distressing for the patient. The same explanation is given for symptoms of vestibulo-cochlear (VIIIth) nerve involvement, such as tinnitus, sensorineural hearing loss, nystagmus, nausea, and vertigo.⁴ Occasionally, facial palsy can accompany zoster infection of C2 and C3.

Management

Herpes zoster infection is usually treated with the antiviral drug acyclovir. The mode of action of the drug is to interfere with the viral DNA polymerase, thereby inhibiting viral replication.² Some clinicians, however, advocate a combined regimen of acyclovir and prednisolone.^2-3-9 The acyclovir covers the possibility of reactivation of herpes simplex within the geniculate ganglion as well as herpes zoster. Steroids help to reduce the inflammatory response and oedema within the bony facial canal. No randomised trial has yet been done to clarify this treatment uncertainty.

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