How do you confirm a diagnosis of paralytic illness?

Confirming Paralytic Illness

The diagnosis of paralytic illness is confirmed through a systematic clinical assessment that identifies the pattern of weakness, followed by targeted ancillary testing including cerebrospinal fluid (CSF) analysis and electrodiagnostic studies, with the specific findings distinguishing between different etiologies such as Guillain-Barré syndrome, Bell's palsy, or anterior horn cell disease.

Clinical Assessment Framework

History and Physical Examination

A thorough history and physical examination must assess the onset, distribution, and progression of weakness to exclude identifiable causes and guide further testing 1.

Key historical features to document:

• Onset timing: Acute onset over hours to days suggests Guillain-Barré syndrome (GBS), while onset beyond 72 hours may indicate tumor or infection 1, 2
• Pattern of weakness: Ascending symmetric paralysis is typical of GBS, while unilateral facial weakness suggests Bell's palsy 1, 3
• Associated symptoms: Presence of dizziness, dysphagia, or diplopia suggests diagnoses other than isolated peripheral nerve disorders 1, 4
• Sensory symptoms: Pure motor weakness with areflexia but no sensory deficits may indicate anterior horn cell disease, while paresthesias and sensory loss suggest GBS 1, 5
• Preceding illness: Gastrointestinal or respiratory infection 1-4 weeks prior supports GBS diagnosis 1, 6

Distinguishing Clinical Patterns

For facial paralysis specifically:

• Bell's palsy involves both upper and lower face (cannot raise eyebrow or wrinkle forehead), while stroke spares the forehead 2
• No other neurological deficits (limb weakness, sensory changes) should be present in Bell's palsy 2
• Bilateral facial weakness is extremely rare in Bell's palsy and suggests GBS or sarcoidosis 2

For limb paralysis:

• Symmetric ascending weakness with areflexia indicates GBS 1, 6
• Asymmetric focal weakness with preserved reflexes suggests anterior horn cell disease (poliomyelitis-like syndrome) 5, 7
• Rapid ascending quadriplegia can mimic GBS but may represent West Nile virus poliomyelitis 7

Ancillary Testing

Cerebrospinal Fluid Analysis

CSF examination is essential to rule out alternative causes and support the diagnosis of GBS 1.

Key findings:

• Albumino-cytological dissociation (elevated protein with normal cell count) is classic for GBS, but protein is normal in 30-50% of patients in the first week 1
• Marked pleocytosis (>50 cells/μl) suggests leptomeningeal malignancy or infectious/inflammatory polyradiculitis, not GBS 1
• Mild pleocytosis (10-50 cells/μl) is compatible with GBS but should prompt consideration of infectious causes 1

Electrodiagnostic Studies

Electrodiagnostic testing is not required for diagnosis but is recommended to support the diagnosis and distinguish between different paralytic syndromes 1.

Distinguishing patterns:

• GBS: Prolonged or absent F-waves, conduction block, temporal dispersion, and slowed conduction velocities; sensory nerve action potentials may be reduced 1
• Anterior horn cell disease: Normal sensory potentials, low-amplitude motor potentials with normal conduction velocities, widespread fibrillation potentials on EMG 5, 7, 8
• Bell's palsy with incomplete paralysis: Electrodiagnostic testing should not be performed 1
• Bell's palsy with complete paralysis: Electrodiagnostic testing may be offered as an option 1

Laboratory Testing

Routine laboratory testing is not indicated unless specific conditions are suspected based on history and examination 1, 4.

Targeted testing when indicated:

• Complete blood count, glucose, electrolytes, kidney and liver function: To exclude metabolic or electrolyte causes of weakness 1
• Lyme disease serology: In endemic areas where Lyme can cause up to 25% of facial paralysis cases 1, 4
• Anti-ganglioside antibodies: Limited diagnostic value; positive results can help when diagnosis is in doubt, but negative results do not rule out GBS 1
• Anti-GQ1b antibodies: Found in up to 90% of Miller Fisher syndrome cases, providing greater diagnostic value for this variant 1

Diagnostic Imaging

Routine diagnostic imaging is not recommended for Bell's palsy or typical GBS presentations 1.

Imaging is indicated when:

• Unilateral paresthesias without clear peripheral cause warrant brain and spine MRI with contrast to rule out central lesions 4
• Atypical features suggest tumor, stroke, or other structural pathology 1, 2

Common Pitfalls

Do not wait for antibody test results or CSF protein elevation before initiating treatment in suspected GBS 1. Normal CSF protein in the first week does not exclude the diagnosis, and treatment delay worsens outcomes.

Do not diagnose Bell's palsy if other neurological deficits are present 2. The presence of limb weakness, sensory changes beyond the face, or bilateral facial weakness requires consideration of alternative diagnoses including GBS, stroke, or brainstem pathology.

Do not assume all acute flaccid paralysis is GBS 5, 7, 8. Anterior horn cell diseases (including West Nile virus poliomyelitis) present with normal sensory studies, preserved or brisk reflexes initially, and asymmetric weakness patterns that distinguish them from typical GBS.