This week in Morning Report we reviewed an approach to a patient with cranial nerve 7 palsy (or facial nerve palsy) following tick bite during a camping trip. We discussed how to differentiate LMN from upper motor neuron (UMN) pathology. We also discussed the spectrum of Lyme disease, and a brief introduction to treatment, prevention, and prophylaxis. See summary below:
1. Differentiating UMN from LMN Lesions
To help differentiate, the innervation to the muscles of the upper face originates from both sides of the cortex. However, the innervation to the to the muscles of the lower face comes from the contralateral side of cortex. If there is a cortical injury, there is weakness in the contralateral face.
In the setting of facial nerve injury, the entire ipsilateral face is weak – see image below, the weakness includes frontalis and orbicularis oculi muscles which are spaced in central or UMN lesions.
The facial nerve is responsible for innervating muscles of facial expression, sensation from the external auditory canal, pinna, mastoid, and mucosa of the palate, taste anterior two thirds of the tongue, and the lacrimal gland, minor salivary glands. Thus to help differentiate, these other features can be assessed on history or physical examination.
Further, in UMN lesions, specifically localizing to the pons, there might be some neighbouring signs that can clue you in including ipsilateral horizontal gaze palsy, ipsilateral 6th nerve palsy, intranuclear ophthalmolplegia due to involvement of ipsilateral medial longitudinal fasciculus, ipsilateral facial numbness due to involvement of the descending tract of CN V, or contralateral hemiparesis.
2. Differential diagnosis for facial nerve palsy
Bell’s palsy is the term for idiopathic cranial nerve palsy or sometimes if attributed to possible viral syndrome. The differential diagnosis of a Bell’s palsy is listed below:
Mobius syndrome (rare birth defect caused by the absence or underdevelopment of 6th or 7th cranial nerve)
|Trauma||Basilar skull fracture|
|Myopathy or related to Neuromuscular junction||Myotonic dystrophy|
– HIV, Zika, EBV
– Spirochete (syphilis, lyme disease)
Geniculate zoster (Ramsay Hunt syndrome)
Osteomyelitis of skull base
Granulomatosis with polyangiitis
Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)
|Idiopathic or Other||Idiopathic intracranial hypertension|
|Toxin Related||Wernicke encephalopathy|
Ethylene glycol ingestion
Given that there might not be other clinical features to suggest Lyme disease before or at the time of facial palsy (ie there might not be erythema migrans or other features), and serologic evidence can lag behind clinical manifestations, the decision to treat is based on index of suspicion.
Of note, routine testing for Borrelia burgdorferi is not recommended for patients with idiopathic CN VII palsy or Bell’s palsy in the absence of additional symptoms of Lyme disease. Routine testing for diabetes mellitus or insulin resistance is also not recommended in patients with Bell’s palsy in the absence of other indications.
In our morning report case of a patient who had a history of recent tick bite and camping in an area with high prevalence of Lyme, and the presence of facial nerve palsy, they were managed with a working diagnosis early disseminated Lyme disease.
3. Understanding Lyme Disease
Lyme is a spirochete, Borrelia Burgdorferi is transmitted via the blacklegged tick, Ixodes scapularis. The life cycle of Ixodes is outlined below. Both nymphs and the adult can transmit infection. The larvae hatch in the summer when they may feed on a small mammal infected with Borrelia Burgdorferi. The larvae survive the winter and then the following spring develop into nymphs, and can transmit infection. The nymphs become adults in the fall and attach to large animals during the winter and the females lay eyes the following spring.
The spectrum of Lyme disease includes a few categories outlined below:
|Early localized||Early disseminated||Late|
|Erythema migrans (typical rash seen in Lyme disease) (see image below)||Multiple erythema migrans|
Isolated CN palsy
Acrodematitis chronica atrophicans (Fibrosing skin condition)
4. Treatment for Lyme Disease
Treatment of Lyme disease as per the 2020 guidelines is outlined below:
Counselling around doxycycline includes discussing the risk of photosensitivity and encouraging use of sunscreen/skin protection, GI upset, and avoid taking the medication with dairy products.
In the setting of neurological Lyme disease with cranial nerve palsy, recommend eye care to prevent corneal injury is recommended as well as the use of artificial tears during waking hours, protective glasses/goggles or eye patch, and ointment of artificial tears during sleep.
5. Prevention and Prophylaxis for Lyme Disease
Prevention for Lyme disease includes the following:
- Personal protective measures
- Avoiding risk habitats
- Wear light-coloured clothing
- Wear long sleeves and pants
- Tuck pants into socks or footwear
- Wear permethrin-treated clothing
- As per the guidelines for the prevention of tick bites, N,N-Diethylmeta-toluamide (DEET), picaridin, ethyl-3-(N-n-butyl-Nacetyl) aminopropionate (IR3535), oil of lemon eucalyptus (OLE), p-methane-3,8-diol (PMD), 2-undecanone, or permethrin (the latter for application to gear or clothing only) are recommended.
Prophylaxis for Lyme disease should be initiating if the following three criteria are met AND if it is within 72 hours of tick removal:
a) identified as Ixodes vector species
b) bite occurred in a highly endemic area (consult state health data)
AND c) attached for ≥36 hours
Prophylaxis is achieved with a single dose of oral doxycycline within 72 hours of tick removal over observation. Prophylactic doxycycline is given as a single oral dose, 200 mg for adults and 4.4 mg/kg (up to a maximum dose of 200 mg) for children.
- Reich SG. Bell’s Palsy. Continuum (Minneap Minn). 2017 Apr;23(2, Selected Topics in Outpatient Neurology):447-466. doi: 10.1212/CON.0000000000000447. PMID: 28375913.
- 2020 guidelines on the prevention diagnosis and treatment of lyme disease – https://www.idsociety.org/practice-guideline/lyme-disease/
- AAFP article on Bell’s palsy https://www.aafp.org/afp/2014/0201/p209.html
- Lyme disease article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3652387/ Murray TS, Shapiro ED. Lyme disease. Clin Lab Med. 2010;30(1):311-328. doi:10.1016/j.cll.2010.01.003
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