Toxicology – Ascending Paralysis

Definition

Ascending paralysis is progressive flaccid weakness beginning in the lower extremities and moving upward toward the trunk and upper extremities. Severe cases can involve bulbar, facial, and respiratory muscles.

Because respiratory weakness can progress rapidly, ascending paralysis should be considered a potential neurologic emergency.

Major Causes

Important causes include:

Nontoxicologic

• Guillain–Barré syndrome (GBS) — the most important common cause
• Acute intermittent porphyria (AIP)
• Spinal cord disease or compression

Toxicologic

• Tick paralysis
• Tetrodotoxin
• Severe arsenic poisoning
• Karwinskia humboldtiana (coyotillo) poisoning
• Selected toxic neuropathies

Other disorders can cause weakness but follow different patterns. For example, botulism classically produces descending rather than ascending paralysis.

Guillain–Barré Syndrome

GBS is an acute immune-mediated peripheral neuropathy.

It commonly follows an infection, particularly:

• Campylobacter jejuni
• Cytomegalovirus
• Epstein–Barr virus
• Other respiratory or gastrointestinal infections

The classic presentation is:

• Symmetric progressive weakness
• Reduced or absent deep-tendon reflexes
• Weakness beginning in the legs
• Relatively mild sensory symptoms

Cranial nerves may also become involved, producing facial or bulbar weakness.

Autonomic dysfunction can cause:

• Tachycardia or bradycardia
• Hypertension or hypotension
• Dysrhythmias
• Urinary retention

Tick Paralysis

Certain ticks produce a neurotoxin capable of causing:

• Progressive symmetric weakness
• Reduced or absent reflexes
• Ascending flaccid paralysis
• Respiratory weakness in severe cases

Sensory function and mental status are generally preserved.

A careful skin and scalp examination for an attached tick is therefore important.

Removal of the causative tick usually leads to improvement, although respiratory support may temporarily be required.

Tetrodotoxin Poisoning

Tetrodotoxin is associated particularly with certain marine animals, including pufferfish.

Mechanism

Tetrodotoxin blocks voltage-gated sodium channels, preventing normal action-potential propagation.

Clinical features can include:

• Perioral and peripheral paresthesias
• Nausea and vomiting
• Weakness
• Dysphagia
• Cranial nerve abnormalities
• Progressive paralysis
• Respiratory failure

Neurologic effects can develop rapidly after significant exposure.

Arsenic

Severe arsenic poisoning can produce a painful sensorimotor peripheral neuropathy.

Early systemic toxicity may include:

• Severe nausea and vomiting
• Abdominal pain
• Profuse diarrhea
• Cardiovascular instability

Neurologic manifestations can later include:

• Painful paresthesias
• Sensory loss
• Reduced reflexes
• Progressive weakness
• Occasionally ascending paralysis

Acute Intermittent Porphyria

AIP can produce a motor neuropathy that occasionally progresses to severe paralysis.

An acute attack may include:

• Severe abdominal pain
• Nausea and vomiting
• Tachycardia
• Hypertension
• Psychiatric or behavioral manifestations
• Peripheral neuropathy
• Motor weakness
• Hyponatremia

Urinary porphobilinogen (PBG) is an important diagnostic test during a suspected acute attack.

Clinical Features

The characteristic neurologic pattern is:

• Symmetric lower-extremity weakness
• Progression toward the trunk and arms
• Reduced or absent reflexes
• Possible mild paresthesias
• Eventual bulbar or facial involvement
• Respiratory muscle weakness in severe disease

The associated symptoms help identify the underlying cause.

Respiratory Assessment

The most immediately dangerous complication is neuromuscular respiratory failure.

Patients require repeated assessment of:

• Respiratory rate and effort
• Oxygenation
• Ability to handle secretions
• Cough strength
• Bulbar function
• Objective respiratory muscle strength, such as serial forced vital capacity and inspiratory pressure measurements

A normal pulse oximetry reading does not reliably exclude impending ventilatory failure, because oxygenation may remain normal until respiratory weakness becomes advanced.

Airway management should therefore be based on the overall clinical trajectory rather than waiting for a single rigid vital-capacity threshold.

Diagnostic Evaluation

Testing is directed toward the suspected cause.

Possible investigations include:

• Electrolytes
• Calcium and magnesium
• Renal function
• ECG and cardiac monitoring
• Blood gas when respiratory failure is suspected
• Serial respiratory function measurements

Additional targeted tests may include:

• Blood lead concentration
• Arsenic testing
• Urinary porphobilinogen for suspected AIP
• Cholinesterase testing when organophosphate poisoning is suspected
• Nerve-conduction studies/electromyography
• Neuroimaging when spinal cord or CNS pathology is possible

GBS Diagnosis

Lumbar puncture classically demonstrates:

Elevated CSF protein with relatively few white blood cells

This is called albuminocytologic dissociation.

However, CSF protein may still be normal early in the illness, so a normal early lumbar puncture does not exclude GBS.

Differential Diagnosis

Important alternatives include:

• GBS
• Tick paralysis
• Tetrodotoxin poisoning
• Acute porphyria
• Severe toxic neuropathy
• Electrolyte abnormalities
• Myasthenia gravis
• Spinal cord disease
• Botulism

Botulism distinction: botulism typically begins with cranial nerve dysfunction and produces symmetric descending paralysis.

Management

The first priority is respiratory and supportive care.

Important measures include:

• Frequent neurologic reassessment
• Close respiratory monitoring
• Cardiac monitoring when autonomic instability is possible
• Early airway support when respiratory or bulbar weakness progresses
• Identification and treatment of the underlying cause

Patients with significant progressive ascending paralysis generally require hospital admission and close monitoring, often in an intensive-care setting.

Cause-Specific Treatment

GBS

• IV immunoglobulin (IVIG) or
• Plasma exchange

Both are established disease-modifying treatments. Corticosteroids alone are not effective treatment for typical GBS.

Tick paralysis

• Locate and completely remove the tick.
• Continue respiratory support when necessary.

AIP

• Remove precipitating factors.
• Provide supportive care.
• Intravenous hemin is the major specific therapy for significant acute attacks.
• Carbohydrate supplementation may be useful in selected mild attacks but should not delay hemin when significant neurologic disease is present.

Heavy-metal poisoning

• Remove the exposure.
• Appropriate chelation may be indicated depending on the metal and severity.

Tetrodotoxin

• No established specific antidote.
• Treatment is primarily meticulous supportive and respiratory care.

Decontamination

Older references recommended routine gastric lavage for some toxic ingestions. This is not standard modern practice.

Activated charcoal may occasionally be considered after an appropriate recent ingestion when the substance is adsorbed by charcoal and the airway is adequately protected.

Decontamination should never delay stabilization of airway, breathing, and circulation.

Key Points

• Ascending paralysis = weakness beginning in the legs and progressing upward.
• GBS is the major common cause and typically produces symmetric weakness with reduced or absent reflexes.
• Tick paralysis can closely resemble GBS; examine the entire skin and scalp.
• Tetrodotoxin blocks voltage-gated sodium channels and can rapidly cause paralysis and respiratory failure.
• Severe arsenic poisoning can produce a painful peripheral neuropathy with progressive weakness.
• Botulism usually causes descending, not ascending, paralysis.
• Albuminocytologic dissociation supports GBS, but it may be absent early.
• Respiratory deterioration can occur before major abnormalities appear on pulse oximetry.
• Progressive bulbar or respiratory weakness requires early airway planning and intensive monitoring.