Parainfectious and Postinfectious Neurologic Syndromes

Facial Nerve Palsy

One of the most common para infectious neurologic syndromes is inflammation of the peripheral facial nerve (cranial nerve VII). Clinically, this presents as a relatively acute onset of unilateral facial weakness. Associated symptoms can include retro-mastoid pain, hyperacusis, and abnormal taste. When no etiology is identified, the condition often is referred to as Bell palsy , which is the case in about 50% of patients suffering from unilateral facial palsy. One study reported an incidence of 4.2 per 100,000 children aged <10 years, increasing to 15.3 per 100,000 in children aged 10–20 years. There is no sex difference, but seasonal differences may be seen depending on the associated infectious agent.

There are two proposed pathologic mechanisms, both leading to edema and entrapment of the nerve in the facial canal. The most likely explanation is direct inflammation of the nerve. Magnetic resonance imaging (MRI) can show gadolinium enhancement of the nerve , and pathologic studies describe lymphocytic infiltration and associated demyelination or axonal degeneration. Another possibility is that increased capillary permeability, as occurs in diabetes, leads to edema and compression of the nerve’s microcirculation. This mechanism is supported by the finding that patients with diabetes are 2.5 times more likely to develop Bell palsy than people without diabetes.

Herpes simplex virus (HSV) has been the most frequent virus associated with an acute peripheral facial nerve palsy. Other viruses, including Epstein-Barr virus (EBV), human herpes virus 6, enteroviruses, and hepatitis B virus, have also been implicated. Ramsay Hunt syndrome, a rare complication of latent varicella-zoster virus (VZV) infection, is defined as an acute peripheral facial nerve palsy associated with an erythematous vesicular rash of the skin of the ear canal, auricle (also termed herpes zoster oticus ), or mucous membrane of the oropharynx. Borrelia burgdorferi infection (Lyme disease) also can also cause facial palsy, which can develop without a recognized tick bite or erythema migrans. In one Lyme disease endemic area, over one-third of individuals aged ≤20 years evaluated in the emergency department with facial palsy were found to have Lyme disease. Lyme disease-associated facial palsy is often bilateral, associated with headache and fever, and typically occurs from May through October. Respiratory viruses also are implicated as a cause. In a recent European cohort, 15% of children presenting with unilateral facial weakness were found to have a respiratory infection.

Treatment is aimed at the underlying etiology, but good eye care is important to protect the cornea because of weak eye closure. Bacterial causes should be treated with appropriate antibiotics. Cases due to Lyme disease should be treated with doxycycline or amoxicillin for 14 to 21 days to prevent late disease; however, treatment has no effect on resolution of the facial nerve palsy. Most palsies resolve without treatment. A meta-analysis of adults and children with Bell palsy demonstrated a 17% improvement with corticosteroid treatment compared with no treatment. Since many cases are thought to be associated with HSV infection, acyclovir/valacyclovir is often advocated but this is controversial. The addition of an antiviral agent to corticosteroid therapy, even when used in the first 72 hours of onset of illness, does not appear to improve outcome. Anti-viral treatment should be given in certain clinical situations, particularly in Ramsay Hunt syndrome. Early referral to plastic surgery and facial nerve rehabilitation should be considered in patients with incomplete facial nerve function recovery.

Optic Neuritis

The second most common cranial nerve to be affected by para infectious demyelination is the optic nerve. Optic neuritis has been reported to have an incidence of 0.2 per 100,000 in Canadian children, similar to that of ADEM and transverse myelitis. Females are more commonly affected than males.

In children, optic neuritis can be unilateral or bilateral, and typically manifests with reduced vision (e.g., blurred or “foggy” vision) and pain with eye movement. Clinical examination reveals a relative afferent pupillary defect of the most affected eye, and optic disc swelling can be visualized on fundoscopic examination in many cases.

Optic neuritis can be accompanied by other neurologic signs or symptoms, as is seen in ADEM, or can be the heralding manifestation of a demyelinating disease such as multiple sclerosis, anti-myelin oligodendrocyte glycoprotein disease, or neuromyelitis optica (Devic disease). Differentiating amongst the demyelinating diagnoses is imperative as long term treatment considerations vary considerably. ^, However, the majority of optic neuritis cases occur after an antecedent infection or following vaccination. ^,

Brain MRI is recommended for patients with isolated optic neuritis. Cerebrospinal fluid (CSF) examination should be considered to examine for oligoclonal bands and other markers of inflammatory or infectious disease. Serum antibody studies for aquaporin 4 IgG (neuromyelitis optica) and anti-myelin oligodendrocyte glycoprotein IgG should be completed. An ophthalmologic consultation should be considered.

Bartonellosis is an infectious cause of isolated optic neuritis and may occur with regional lymphadenopathy and fever. Mycobacterium tuberculosis , Treponema pallidum , and Borrelia burgdorferi also are reported to cause optic neuritis, papillitis, and optic neuropathy. ^, Arboviruses, including West Nile virus and chikungunya, ^, have also been associated with optic neuritis. Animal roundworms (e.g., Toxocara canis and Baylisascaris procyonis ) are rare causes of optic neuritis. When these nematodes invade the eye, a neuroretinitis also can occur and the worm itself is sometimes visualized in the retina. Angiostrongylus cantonensis (a cause of eosinophilic meningitis) is found in Southeast Asia, the South Pacific, Australia, the Caribbean, and some areas of the US (e.g., Louisiana and Hawaii) and can cause optic neuritis.

The typical treatment for optic neuritis is a several-day course of intravenous corticosteroids. Additional treatment with specific antimicrobial therapy may be needed depending on the cause. While steroid treatment hastens visual recovery, it does not change the eventual visual outcome. The prognosis is generally good for patients with optic neuritis, with visual acuity at or near baseline in at least 70% of patients.