Incomplete Bell’s Palsy Following Influenza Vaccination in a 7-Month-Old

Case Presentation

Written informed consent for all subsequent patient information, photographs, and clinical images was provided by the patient’s legal guardians.

A previously healthy developmentally typical 7-month-old male presents to the Emergency Department with acute onset right-sided facial weakness that parents first noticed earlier in the morning. His exam is notable for subtle right nasolabial fold flattening and drooping of the right corner of his mouth (Figure 1). He is able to close both eyelids completely and lift both eyebrows (Figure 2). Of note, he received his initial intramuscular inactive quadrivalent influenza vaccine at his 6-month well-child visit according to the Centers for Disease Control and Prevention (CDC) recommendations and had just received an appropriate booster dose of the intramuscular inactivated quadrivalent influenza vaccine 6 days prior to presentation. He has no past medical history, does not take any medications or supplements routinely, and has not traveled recently. Family history is negative for any neurological, bleeding, or clotting disorders.

Figure 1.

Drooping of the right corner of the mouth.

Figure 2.

Flattening of the right nasolabial fold and drooping of corner of right mouth with preserved ability to raise both eyebrows bilaterally.

Magnetic resonance imaging (MRI) of the brain is performed due to concern for supranuclear involvement of the facial nerve in the setting of bilateral preserved forehead movements. The MRI demonstrated slight asymmetric increase in enhancement of the tympanic and mastoid segments of the right facial nerve (Figure 3). Labs were notable for a negative severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) polymerase chain reaction (PCR) and a negative serum herpes simplex virus (HSV) 1/2 PCR. He is not evaluated for Lyme disease, given the absence of erythema migrans by history and exam. He has no known exposure to any ticks, especially those from a Lyme endemic region. He is discharged home with a diagnosis of right facial nerve paresis. He is evaluated by both his pediatrician and a pediatric neurologist following discharge with complete resolution of his facial nerve paresis within 48 hours of symptom onset. He has not had further recurrence of symptoms even with continued yearly influenza immunizations and continues to grow and develop normally.

Figure 3.

MRI brain with and without contrast demonstrating asymmetric increase in enhancement of the tympanic portion of the right facial nerve as indicated by the red arrow. The tympanic portion of the left facial nerve has normal enhancement as indicated by the blue arrow.

Although not conclusive, the close temporal association between his recent inactivated quadrivalent influenza vaccine and onset of facial nerve paresis suggested a possible underlying immunologic reaction.

Discussion

Cranial nerve VII is responsible for the motor innervation of the muscles of the face and parasympathetic innervation of the lacrimal gland and the submandibular gland. When patients present with facial asymmetry due to weakness of the facial muscles, this may be secondary to either a supranuclear or infranuclear etiology. The muscles of the upper portion of the face are innervated by both sides of the brain. Due to crossing of motor fibers at the level of the facial nucleus, patients with supranuclear lesions will have facial weakness but preserved ability to furrow their brow bilaterally.^1,2 The muscles of the lower portion of the face are supplied solely by motor fibers from the contralateral side; patients with infranuclear lesions will have facial weakness with decreased forehead movements.^1,2

Supranuclear causes of facial palsy include any brain lesion that impacts the connection between the cerebral cortex and the facial nucleus. These include thromboembolic or hemorrhagic events and malignancies and would be expected to present with additional neurological deficits warranting emergent imaging, evaluation, and treatment. ²

Infranuclear pathologies affect the facial nerve as it courses through the fallopian canal in the temporal bone; its long intraosseous course makes it more vulnerable to injury. ² Causes can include infections (eg, Lyme disease, acute otitis media, and mastoiditis), trauma, ischemia, neoplasms, and iatrogenic causes (eg, surgical procedures and forceps delivery).^1,2 Certain congenital disorders including Moebius syndrome and Melkersson-Rosenthal syndrome also present with facial nerve palsies as one of their core physical exam findings. ² Bell’s palsy is an idiopathic infranuclear facial nerve palsy and is considered a diagnosis of exclusion. ²

Bell’s palsy is the most common disorder of the facial nerve with an estimated incidence in the pediatric population ranging from 2.7 per 100 000 person-years to upward of 18.8 per 100 000 person-years.^3,4 Multiple studies have documented a lower incidence in young children (0-9 years) compared with older children (10-18 years).^3-6 Symptomatology varies depending on which branches of the facial nerve are involved and can vary from partial weakness (paresis) to a complete paralysis. ¹ One prospective study from Switzerland noted 65% of their patients presenting with a diagnosis of Bell’s palsy had paresis and only 35% had complete paralysis of the facial nerve. ⁷ Typical symptoms include ipsilateral decreased forehead movement, flattening of the nasolabial fold, drooping of the mouth, difficulty in closing the eyelids, hyperacusis, decreased lacrimation, and changes in taste. ¹ The House-Brackmann Facial Nerve Grading System can be used to grade facial nerve function but can be challenging to utilize in young children and infants. ⁸ Grades II to V describe the incomplete facial nerve paresis, while Grade VI describes the complete paralysis of the facial nerve. Patients with Grades II to III, indicating mild-to-moderate dysfunction, may still be able to maintain some forehead movements. ⁸

In the absence of other worrisome neurological findings, routine imaging with computed tomography (CT) or MRI for suspected Bell’s palsy is generally not recommended. Imaging is indicated in the setting of progressive or recurrent facial nerve palsies or in the absence of spontaneous recovery of facial nerve function by 3 months. ⁹ Enhancement of the tympanic, mastoid, and labyrinthine segments of the facial nerve is typically seen on MRI. However, the pattern and extent of facial nerve enhancement on MRI do not correlate closely with the clinical presentation and the House-Brackmann facial nerve grade.^10,11

The exact pathophysiology of Bell’s palsy remains unclear. Acute demyelination, reactivation of latent herpes virus, and immunologic responses following vaccinations have all been proposed to cause inflammation of the facial nerve; the subsequent edema causes compression along the narrowest portion of the fallopian canal resulting in temporary loss of function. ¹

Multiple studies in the adult population have described a potential temporal association between influenza immunizations and Bell’s palsy with onset as early as 3 days up to 60 days postimmunization.^12-15 Using data from the Vaccine Adverse Event Reporting System (VAERS) database, influenza vaccination has been associated with a 2-fold higher probability of subsequent facial paralysis being reported compared with other vaccines. ¹⁴ A study from Switzerland involving a new intranasal inactivated virosomal-subunit influenza vaccine introduced in 2000 saw a significant association between the vaccine and development of Bell’s palsy; the relative risk was estimated to be 19 times the risk of controls within the first 3 months following receipt of the vaccine. ¹⁵ It is important to emphasize these studies only highlight a potential temporal association between immunizations and development of Bell’s palsy; this does not mean the vaccines themselves caused Bell’s palsy.

This signal of a temporal association between influenza vaccine and Bell’s palsy is much less clear in the pediatric population. A study from the early 2000s using data from the VAERS only noted 5 out of 197 affected individuals were less than 18 years of age. ¹² A more recent study analyzing data from VAERS between 2015 and 2019 confirmed these earlier findings with the average age of affected patients in the fourth to fifth decade of life with no cases reported in patients under the age of 28 years. ¹⁴ The authors of both studies are clear about the limitations of relying on data derived from VAERS which depends on passive reporting and may be neither comprehensive nor free of bias.

Kaiser Permanente Northern California (KPNC) performed a retrospective study looking at all individuals <18 years of age from 2001 to 2006 who were diagnosed with Bell’s palsy. Results did not demonstrate any statistical association with trivalent inactivated influenza vaccination in the preceding 56 days. ¹⁶ A prospective observational cohort study was performed following KPNC patients aged 2 to 49 years in 2013 to 2014 to assess the safety of quadrivalent live attenuated influenza vaccine (Q/LAIV) compared with quadrivalent inactivated influenza vaccine and unvaccinated controls. The incidence of Bell’s palsy was one of the prespecified events of interest, and no cases were identified in the predefined risk interval of 42 days postimmunization. ¹⁷ However, neither of these KPNC studies is generalizable to this particular patient. The earlier KPNC study evaluated a trivalent inactivated influenza vaccine no longer in clinical use, and the subsequent study did not include patients under the age of 2 years as they were primarily evaluating the safety of the Q/LAIV which is not used in infants. Thus, additional studies are needed to evaluate if there is a connection between rare immunological reactions causing Bell’s palsy following influenza vaccination, particularly in infants.

The health burden of influenza cannot and should not be underestimated. Worldwide, 10% to 15% of infected children each year will require some form of medical treatment, and over 300 000 children under the age of 1 year and 870 000 children under the age of 5 years require hospitalization annually.^18,19 Given its track record of safety and efficacy, an age-appropriate influenza vaccine should continue to be recommended for all children 6 months and older. ²⁰

Treatment/Management

There is no known preventative or curative treatment for Bell’s palsy. The use of antiherpetic antivirals has fallen out of favor as previous studies have not demonstrated conclusive benefit. ²¹ Several recent studies have supported the continued use of corticosteroids for improved recovery rates of facial nerve function in adults. ²¹ Data from pediatric studies have been less conclusive with several demonstrating no clear difference in recovery rates for children treated with corticosteroids compared with no treatment.^22,23 Fortunately, the prognosis for children with Bell’s palsy is excellent; multiple studies report greater than 95% of affected individuals will achieve complete facial nerve function recovery within 3 months.^22,23 The recurrence risk is commonly reported to be between 5% and 10%.^24,25

Educational Objectives

• Depending on the branches and degree of facial nerve involvement, Bell’s palsy can present as a spectrum ranging from partial weakness to a complete paralysis. The variable physical exam findings can make determining infranuclear from supranuclear etiologies more challenging. Findings may be more subtle in the pediatric population as patients may be unable to report subjective sensory changes.

• Although Bell’s palsy has been described as having a clear temporal association with influenza immunization in adults, this phenomenon has not been previously well-documented or reported in the pediatric population and further studies are needed.

• Given the disease burden of influenza and the proven safety record of influenza vaccines, physicians should continue to strongly encourage influenza immunization for all children 6 months and older.

Author Contributions

ES: performed literature review, drafted and edited the manuscript. CM: performed literature review, drafted and edited the manuscript. HW: provided clinical care to the patient, drafted and edited the manuscript. LM: performed literature review, drafted and edited the manuscript.