What is Intermediate Syndrome (Organophosphate Poisoning)?

From the Guidelines

Intermediate Syndrome is a condition that occurs after Organophosphate Poisoning, characterized by muscle weakness, paralysis, and respiratory failure, typically developing 24-96 hours after exposure.

Key Features of Intermediate Syndrome

• It is a result of the irreversible inhibition of the enzyme acetylcholinesterase (AChE) by organophosphate compounds, leading to an accumulation of acetylcholine in the nervous system 1.
• The symptoms of Intermediate Syndrome include muscle weakness, paralysis, and respiratory failure, which can be life-threatening if not treated promptly 1.
• The management of Intermediate Syndrome involves supportive care, such as respiratory support and physical therapy, as well as the use of medications like atropine and oximes to treat the underlying organophosphate poisoning 1.

Treatment of Organophosphate Poisoning

• Atropine is a key medication used to treat organophosphate poisoning, as it blocks the parasympathetic effects of acetylcholine and can help to alleviate symptoms like bronchospasm and bradycardia 1.
• Benzodiazepines may also be used to treat seizures and agitation associated with organophosphate poisoning 1.
• Pralidoxime is a medication that can be used to treat organophosphate poisoning, as it can help to reactivate AChE and alleviate symptoms 1.
• Dermal decontamination is an important step in the management of organophosphate poisoning, as it can help to prevent further absorption of the toxin and reduce the risk of secondary exposure to healthcare workers 1.

From the Research

Definition and Characteristics of Intermediate Syndrome

• Intermediate Syndrome (IMS) is a condition that occurs after organophosphate poisoning, typically 2-4 days after exposure 2.
• It is characterized by weakness of the muscles of respiration, proximal limb muscles, and muscles innervated by some cranial nerves 2, 3.
• The syndrome is called "intermediate" because it occurs after the acute cholinergic syndrome but before organophosphate-induced delayed polyneuropathy 2.

Clinical Features and Diagnosis

• The characteristic features of IMS include weakness of the diaphragm, intercostal muscles, and accessory muscles, including neck muscles 2.
• Accompanying features often include weakness of muscles innervated by some cranial nerves 2.
• Electrophysiological studies have revealed three characteristic phenomena: repetitive firing, decrement-increment response, and decrementing response 2, 4, 5.
• Diagnosis of IMS is based on clinical diagnostic criteria, including physical examination and repetitive nerve stimulation (RNS) 5.

Management and Treatment

• Management of IMS is essentially that of rapidly developing respiratory distress and respiratory failure 2.
• Ventilatory care is often required, and delays in instituting ventilatory care can result in death 2.
• The use of depolarizing muscle relaxants, such as suxamethonium, is contraindicated in OP poisoning 2.
• Prophylactic antibiotics are usually not required unless there has been evidence of aspiration of material into the lungs 2.
• Close monitoring of fluid and electrolyte balance, nutrition, and physiotherapy are necessary to minimize discomfort during ventilatory care 2.

Prognosis and Outcome

• Recovery from IMS is normally complete and without any sequelae 2, 3.
• However, some patients may develop delayed neuropathy or other complications, such as pancreatitis 3, 6.
• The usefulness of oximes during IMS remains uncertain, and controlled randomized clinical studies are necessary to evaluate their efficacy 2.