Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (92 page)

   Idiopathic

   Drugs, toxic substances

   Chronic renal failure

   Thyroid disorders

The diagnosis of a mononeuropathy is based on history, neurologic examinations over time evaluation of progression, electrodiagnostic studies, somatosensory potentials, and neuroimaging (MRI).

   Laboratory Findings

Blood tests:

   Fasting glucose and glycohemoglobin in patients with possible diabetic amyotrophy, idiopathic radiculopathy, or polyneuropathy

   Lyme titers in patients with polyradiculopathy, especially in endemic areas

   Genetic tests for hereditary neuropathy with predisposition to pressure palsy for patients with multiple mononeuropathies (usually affecting at least two to three extremities) and Chédiak-Higashi syndrome

Lumbar puncture: Evaluation of CSF is warranted in patients with unusual presentations. CSF should be examined for evidence of inflammation, elevated CSF protein, and serologic testing for Lyme disease, syphilis, and CMV. Cytologic evaluation for tumor cells may be warranted.

FACIAL PALSY (BELL PALSY)

   Definition

Bell palsy is the loss of function of cranial nerve VII resulting in facial paralysis.

   Clinical Presentation

Patients with Bell palsy typically present with the sudden onset (usually over hours) of unilateral facial paralysis and comprise approximately 50% of patients with facial nerve palsy.
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Current research suggests that herpes simplex virus is the etiologic agent causing neural inflammation, demyelination, and palsy.
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Other infectious agents associated with facial palsy include herpes zoster, CMV, Epstein-Barr virus, adenovirus, rubella virus, mumps, influenza B, HIV, and coxsackie virus.
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Lyme disease may produce bilateral palsy. Early negative blood serology does not exclude the diagnosis. A lymphocyte pleocytosis in the CSF is suggestive, and the finding of specific oligoclonal IgG in the CSF is a sensitive indicator.
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Rickettsial and Ehrlichia infection have also been found in patients with facial palsy.
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Bacterial infections such syphilis, leprosy, diphtheria, catscratch disease,
M. pneumoniae,
and nonspecific local inflammation including otitis media have also been known to cause facial palsy as have some parasitic infections such as malaria. Granulomatous disease such as sarcoidosis should be considered, especially in patients with bilateral facial palsy.

Trauma, tumor (acoustic neuromas [see eBook Figure 4-11], tumors invading the temporal bone), cholesteatoma, and Paget disease of bone should be suspected if the onset of facial palsy is gradual. These can be diagnosed on imaging.

Drug reaction, particularly to dental injections, may cause local facial neuropathy, diagnosed on history. Postvaccinal effect and Guillain-Barré syndrome may cause bilateral facial palsy.

Melkersson-Rosenthal syndrome, a granulomatous disorder of unknown etiology, may display recurrent facial palsy.
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   Laboratory Findings