eMedicine Specialties > Neurology > Inflammatory and Demyelinating Diseases

Bell Palsy: Differential Diagnoses & Workup

Author: Kim Monnell, DO,, Neurology Consulting Staff, Department of Medicine, Bay Pines VA Medical Center
Coauthor(s): Sally B Zachariah, MD, Associate Professor, Department of Neurology, University of South Florida; Director, Department of Neurology, Division of Strokes, Veteran Affairs Medical Center of Bay Pines; Suzan Khoromi, MD, Fellow, Pain and Neurosensory Mechanisms Branch, National Institute of Dental and Cranial Research, National Institutes of Health
Contributor Information and Disclosures

Updated: Oct 26, 2009

Differential Diagnoses

Acute Inflammatory Demyelinating Polyradiculoneuropathy
Low-Grade Astrocytoma
Amyloid Angiopathy
Lyme Disease
Anterior Circulation Stroke
Meningioma
Arsenic
Meningococcal Meningitis
Basilar Artery Thrombosis
Möbius Syndrome
Benign Skull Tumors
Multiple Sclerosis
Brainstem Gliomas
Neurofibromatosis, Type 2
Cerebral Aneurysms
Neurosarcoidosis
Guillain-Barre Syndrome in Childhood
Neurosyphilis
Intracranial Hemorrhage
Tuberculous Meningitis

Other Problems to Be Considered

Basal skull fractures
Barotrauma
Botulism
Carcinomatosis
Carotid disease and stroke
Diphtheria
Facial injuries
Forceps delivery
HIV
Iatrogenic (as in otologic, neurotologic, skull base, or parotid surgery)
Idiopathic
Infection
Intratemporal internal carotid artery aneurysm
Lyme disease
Malignant otitis externa
Meningitis
Mycoplasma pneumonia
Mumps
Parotid tumor
Ramsay Hunt syndrome
Sarcoma
Teratoma
Tetanus
Thalidomide exposure
Trauma
Toxic
Vascular
Wegener vasculitis

Workup

Laboratory Studies

  • In areas where Lyme disease is endemic, Lyme titers (IgM and IgG) should be obtained.
  • Blood glucose or hemoglobin A1c may be obtained to determine if the patient has undiagnosed diabetes.
  • Serum titres (IgM and IgA) for Mycoplasma pneumoniae may be obtained. A study in Germany measured titres in patients with Bell palsy and found that several patients had elevated titres to M pneumoniae, and only 2 of those who tested positive had respiratory symptoms.3  
  • Serum titers for HSV may be obtained, but this is usually not helpful owing to the ubiquitous nature of this virus.

Imaging Studies

  • If the history and physical examination lead to a diagnosis of Bell palsy, then immediate imaging is not necessary.
  • Imaging is not required because most patients with Bell palsy improve within 8-10 weeks. If the paralysis does not improve or worsens, imaging may be useful.
  • The MRI of patients with Bell palsy may show enhancement of the seventh nerve at, or near, the geniculate ganglion. However, if the paralysis progresses over weeks, the possibility is high of a neoplasm compressing the seventh cranial nerve. Tumors that compress or involve the seventh cranial nerve include schwannoma (most common), hemangioma, meningioma, and sclerosing hemangioma.
  • MRI is preferred for imaging the cerebellopontine angle.
  • If the patient has a history of trauma, CT scan of the temporal bone may be required.
  • If the patient has a palpable parotid mass, imaging may be necessary.

Other Tests

  • The following tests may be performed in the office setting. However, they require both the patient's and physician's time. They may be helpful in assessing the extent of the damage to the seventh nerve.
    • The stethoscope loudness test may be used to assess the functioning of the stapedius muscle. The patient wears the stethoscope, and the activated tuning fork is placed at the bell of the stethoscope. The loud sound will lateralize to the side of the paralyzed stapedius muscle
    • The Schirmer blotting test may be used to assess tearing function. The use of benzene will stimulate the nasolacrimal reflex, and the degree of tearing can be compared between the paralyzed and normal sides.
    • Salivary flow also may be tested. The physician places a small catheter into both the paralyzed and normal submandibular glands. The patient is then asked to suck on a lemon, and the salivary flow is compared between the 2 sides. The normal side is the control.
  • Useful tests for evaluation of the function of the facial nerve include nerve conduction testing and EMG.
    • These tests may aid in assessing the outcome of a patient who has persistent and severe Bell palsy. This test is most useful when performed 3-10 days after the onset of paralysis.
    • Nerve conduction responses are abnormal if a difference of 50% in amplitude between the paralyzed and normal side is detected; a difference of 90% between the 2 sides suggests a poorer prognosis.
    • May et al demonstrated that prognosis may be favorable if the motor amplitude of the affected side was greater than 25% of that of the normal side. An incomplete recovery was observed in patients whose results demonstrated less than 25% amplitude on the paralyzed side.4
    • Blink reflexes can be used to measure conduction across the involved segment but they are commonly absent in Bell palsy.
  • Brainstem auditory-evoked response (BAER) may be obtained in patients with peripheral seventh nerve lesions and other neurologic involvement.
    • BAER measures the transmission of response through the brain stem and is effective in detecting, notably, retrocochlear lesions.
    • Hendrix and Melnick evaluated BAER of 17 patients with Bell palsy. They found no evidence of retrocochlear lesions of the auditory system in any of their patients with Bell palsy.5
    • In another study by Shannon et al, BAER was recorded in 27 patients with Bell palsy; only 6 patients had prolonged brainstem transmission but normal auditory function.6
    • These studies were small and do not support routine use of BAER in patients with Bell palsy. However, when a patient presents with multiple cranial neuropathies, ie, of CN VII and VIII, BAER may be useful.

Histologic Findings

A review of 12 autopsy cases of patients with Bell palsy was summarized in Peter Dyck's Peripheral Neuropathy.7 This stated that most cases showed inflammatory changes around the mastoid cells and walls of the arteries. The most common site of involvement was the geniculate ganglion.

Surgical findings described constriction of the nerve at the stylomastoid foramen with swelling of the nerve itself. Microscopic findings showed an inflammatory reaction with infiltration of macrophages on the nerve.

More on Bell Palsy

Overview: Bell Palsy
Differential Diagnoses & Workup: Bell Palsy
Treatment & Medication: Bell Palsy
Follow-up: Bell Palsy
Multimedia: Bell Palsy
References
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Further Reading

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Keywords

Bell's palsy, idiopathic facial paralysis, facial nerve compression, acute unilateral facial paralysis, bilateral facial palsy, Guillain-Barré syndrome, GBS, sarcoidosis, Lyme disease, meningitis, neoplastic meningitis, infectious meningitis, bilateral neurofibromas, neurofibromatosis type 2, ipsilateral facial palsy

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Contributor Information and Disclosures

Author

Kim Monnell, DO,, Neurology Consulting Staff, Department of Medicine, Bay Pines VA Medical Center
Kim Monnell, DO, is a member of the following medical societies: American Academy of Neurology and American Osteopathic Association
Disclosure: Nothing to disclose.

Coauthor(s)

Sally B Zachariah, MD, Associate Professor, Department of Neurology, University of South Florida; Director, Department of Neurology, Division of Strokes, Veteran Affairs Medical Center of Bay Pines
Sally B Zachariah, MD is a member of the following medical societies: American Academy of Neurology, American Heart Association, and American Society of Neuroimaging
Disclosure: none None None

Suzan Khoromi, MD, Fellow, Pain and Neurosensory Mechanisms Branch, National Institute of Dental and Cranial Research, National Institutes of Health
Suzan Khoromi, MD is a member of the following medical societies: American Academy of Neurology, American Pain Society, and International Association for the Study of Pain
Disclosure: Nothing to disclose.

Medical Editor

Milind J Kothari, DO, Professor and Vice-Chair, Department of Neurology, Pennsylvania State University College of Medicine; Consulting Staff, Department of Neurology, Hershey Medical Center
Milind J Kothari, DO is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and American Neurological Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Florian P Thomas, MD, MA, PhD, Drmed, Director, Spinal Cord Injury Unit, St Louis Veterans Affairs Medical Center; Director, National MS Society Multiple Sclerosis Center; Professor, Department of Neurology and Psychiatry, Associate Professor, Institute for Molecular Virology, and Department of Molecular Microbiology and Immunology, St Louis University
Florian P Thomas, MD, MA, PhD, Drmed is a member of the following medical societies: American Academy of Neurology, American Paraplegia Society, and National Multiple Sclerosis Society
Disclosure: Nothing to disclose.

Chief Editor

B Mark Keegan, MD, FRCPC, Assistant Professor of Neurology, College of Medicine, Mayo Clinic; Master's Faculty, Mayo Graduate School; Consultant, Department of Neurology, Mayo Clinic, Rochester
B Mark Keegan, MD, FRCPC is a member of the following medical societies: American Academy of Neurology, American Medical Association, and Minnesota Medical Association
Disclosure: Nothing to disclose.

 
 
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