AUTHOR AND EDITOR INFORMATION

Section 1 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

Background

Pseudocholinesterase deficiency is an inherited enzyme abnormality that results in abnormally slow metabolic degradation of exogenous choline ester drugs such as succinylcholine. A variety of pathologic conditions, physiologic alterations, and medications also can lower plasma pseudocholinesterase activity.

This condition is recognized most often when respiratory paralysis unexpectedly persists for a prolonged period of time following administration of standard doses of succinylcholine. The mainstay of treatment in these cases is ventilatory support until diffusion of succinylcholine from the myoneural junction permits return of neuromuscular function of skeletal muscle. The diagnosis is confirmed by a laboratory assay demonstrating decreased plasma cholinesterase enzyme activity.

Genetic analysis may demonstrate a number of allelic mutations in the pseudocholinesterase gene, including point mutations resulting in abnormal enzyme structure and function and frameshift or stop codon mutations resulting in absent enzyme synthesis. Partial deficiencies in inherited pseudocholinesterase enzyme activity may be clinically insignificant unless accompanied by a concomitant acquired cause of pseudocholinesterase deficiency. Clinically significant effects generally are not observed until the plasma cholinesterase activity is reduced to less than 75% of normal.

Pathophysiology

Pseudocholinesterase is a glycoprotein enzyme, produced by the liver, circulating in the plasma. It specifically hydrolyzes exogenous choline esters; however, it has no known physiologic function.

Pseudocholinesterase deficiency results in delayed metabolism of only a few compounds of clinical significance, including the following: succinylcholine, mivacurium, procaine, and cocaine. Of these, its most clinically important substrate is the depolarizing neuromuscular blocking agent, succinylcholine, which the pseudocholinesterase enzyme hydrolyzes to succinylmonocholine and then to succinic acid.

In individuals with normal plasma levels of normally functioning pseudocholinesterase enzyme, hydrolysis and inactivation of approximately 90-95% of an intravenous dose of succinylcholine occurs before it reaches the neuromuscular junction. The remaining 5-10% of the succinylcholine dose acts as an acetylcholine receptor agonist at the neuromuscular junction, causing prolonged depolarization of the postsynaptic junction of the motor-end plate. This depolarization initially triggers fasciculation of skeletal muscle. As a result of prolonged depolarization, endogenous acetylcholine released from the presynaptic membrane of the motor neuron does not produce any additional change in membrane potential after binding to its receptor on the myocyte. Flaccid paralysis of skeletal muscles develops within 1 minute.

In normal subjects, skeletal muscle function returns to normal approximately 5 minutes after a single bolus injection of succinylcholine as it passively diffuses away from the neuromuscular junction. Pseudocholinesterase deficiency can result in higher levels of intact succinylcholine molecules reaching receptors in the neuromuscular junction, causing the duration of paralytic effect to continue for as long as 8 hours.

This condition is recognized clinically when paralysis of the respiratory and other skeletal muscles fails to spontaneously resolve after succinylcholine is administered as an adjunctive paralytic agent during anesthesia procedures.

Frequency

International

Pseudocholinesterase deficiency is most common in people of European descent; it is rare in Asians.

CLINICAL

Section 3 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

History

A personal or family history of an adverse drug reaction to one of the choline ester compounds, such as succinylcholine, mivacurium, or cocaine, may be the only clue suggesting pseudocholinesterase deficiency.

Physical

No characteristic physical examination findings correlate with the presence of pseudocholinesterase deficiency.

Causes

• Most clinically significant causes of pseudocholinesterase deficiency are due to one or more inherited abnormal alleles that code for the synthesis of the enzyme.
• • These abnormal alleles may result in a failure to produce normal amounts of the enzyme or in production of abnormal forms of pseudocholinesterase with altered structure and lacking full enzymatic function, as described below.
  • Patients with only partial deficiencies of inherited pseudocholinesterase enzyme activity often do not manifest clinically significant prolongation of paralysis following administration of succinylcholine unless a concomitant acquired cause of pseudocholinesterase deficiency is present. The acquired causes of pseudocholinesterase deficiency include a variety of physiologic conditions, pathologic states, and medications listed below.
• Inherited causes of pseudocholinesterase deficiency include the following:
• • The gene that codes for the pseudocholinesterase enzyme is located at the E1 locus on the long arm of chromosome 3, and 96% of the population is homozygous for the normal pseudocholinesterase genotype, which is designated as EuEu.
  • The remaining 4% of the population carries one or more of the following atypical gene alleles for the pseudocholinesterase gene in either a heterozygous or homozygous fashion.

    Table 1. Atypical Gene Alleles for the Pseudocholinesterase Genotype

    Ea	Atypical dibucaine-resistant variant	Point mutation
    Ef	Fluoride-resistant variant	Point mutation
    Es	Silent variant	Frameshift mutation

    *These alleles may occur either in the homozygous form or in any heterozygous combination with each other, with the normal Eu allele, or with a number of additional rare variant abnormal alleles.
  • In individuals with an inherited form of pseudocholinesterase deficiency, only a single atypical allele is carried in a heterozygous fashion, resulting in a partial deficiency in enzyme activity, which manifests as a slightly prolonged duration of paralysis, longer than 5 minutes but shorter than 1 hour, following administration of succinylcholine. Less than 0.1% of the general population carries 2 pseudocholinesterase gene allele mutations that will produce clinically significant effects from succinylcholine lasting longer than 1 hour.
  • One rare variant allele of the pseudocholinesterase gene, designated the C5 variant, actually has higher than normal enzyme activity, resulting in relative resistance to the paralytic effects of succinylcholine.
  • The dibucaine-resistant genetic variant form of pseudocholinesterase is identified by the percent inhibition of hydrolysis of benzyl choline caused by the addition of dibucaine to the pseudocholinesterase enzymatic assay. The dibucaine number is the percent inhibition of hydrolysis of benzyl choline by dibucaine added to the plasma sample. The normal dibucaine number for the homozygous typical genotype (EuEu) is 80%. Individuals homozygous for the atypical dibucaine resistant genotype (EaEa) have a dibucaine number of 20%, which correlates with a marked prolongation of the paralytic effect of standard doses of succinylcholine to well over 1-hour duration. Heterozygotes (EuEa) have intermediate dibucaine numbers and modest prolongation of muscle paralysis with succinylcholine. The EuEa heterozygous genotype is found in 2.5% of the general population, making it more common than all other abnormal pseudocholinesterase genotypes combined.
  • The fluoride-resistant pseudocholinesterase enzyme variant is identified by its percent inhibition of benzyl choline hydrolysis when fluoride is added to the assay. The fluoride number (percentage inhibition of enzyme activity in the presence of fluoride) is 60% for the EuEu genotype and is 36% for the EfEf genotype. This homozygous fluoride-resistant genotype exhibits mild to moderate prolongation of succinylcholine-induced paralysis. The heterozygous fluoride-resistant genotype usually is clinically insignificant unless accompanied by a second abnormal allele or by a coexisting acquired cause of pseudocholinesterase deficiency.
  • The most severe form of inherited pseudocholinesterase deficiency occurs in only 1 in 100,000 individuals who are homozygous for the silent Es genotype, with no detectible pseudocholinesterase enzyme activity. These individuals may exhibit prolonged muscle paralysis for as long as 8 hours following a single dose of succinylcholine. Gene mutations that produce silent alleles are caused by frameshift or stop codon mutations, resulting in no functional pseudocholinesterase enzyme synthesis.
• Acquired causes of pseudocholinesterase deficiency include the following:
• • People, such as neonates, elderly individuals, and pregnant women, with certain physiologic conditions may have lower plasma pseudocholinesterase activity.
  • Pathologic conditions that may lower plasma pseudocholinesterase activity include the following:
    • Chronic infections (tuberculosis)
    • Extensive burn injuries
    • Liver disease
    • Malignancy
    • Malnutrition
    • Organophosphate pesticide poisoning
    • Uremia
  • Iatrogenic causes of lower plasma pseudocholinesterase activity include plasmapheresis and medications such as the following:
    • Anticholinesterase inhibitors
    • Bambuterol
    • Chlorpromazine
    • Contraceptives
    • Cyclophosphamide
    • Echothiophate eye drops
    • Esmolol
    • Glucocorticoids
    • Hexafluorenium
    • Metoclopramide
    • Monoamine oxidase inhibitors
    • Pancuronium
    • Phenelzine
    • Tetrahydroaminacrine

DIFFERENTIALS

Section 4 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

Myasthenia gravis
Phase II neuromuscular block from repeated administration of high-dose succinylcholine

WORKUP

Section 5 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

Lab Studies

• Diagnosis of pseudocholinesterase deficiency is made by plasma assays of pseudocholinesterase enzyme activity.
• • A sample of the patient's plasma is incubated with the substrate butyrylthiocholine along with the indicator chemical 5,5'-dithiobis-(2-nitrobenzoic acid), which will produce a colored product that is assayed using spectrophotometry. The resulting amount of spectrophotometric absorption is proportionate to the pseudocholinesterase enzyme activity that is present in the patient's plasma sample.
  • Because succinylcholine metabolites can interfere with this assay, plasma samples should be collected after muscle paralysis has completely resolved.
  • The dibucaine and fluoride numbers can be determined by repeating this assay in the presence of standard aliquots of either dibucaine (0.03 mmol/L) or fluoride (4 mmol/L) in the reaction mixture to determine the percent inhibition of enzyme activity caused by these agents.
• A simplified screening test of pseudocholinesterase enzyme activity can be performed using the Acholest Test Paper. When a drop of the patient's plasma is applied to the substrate-impregnated test paper, a colorimetric reaction occurs. The time it takes the exposed Acholest Test Paper to turn from green to yellow is inversely proportional to the pseudocholinesterase enzyme activity in the plasma sample.

  Table 2. Reaction Times for Acholest Test Paper

  Reaction Time	Pseudocholinesterase Enzyme Activity
  <5 min	Above normal
  5-20 min	Normal
  20-30 min	Borderline low
  >30 min	Below normal

Imaging Studies

• No imaging studies aid in the diagnosis of pseudocholinesterase deficiency.

Other Tests

• The complete DNA sequence and amino acid structure of both the normal pseudocholinesterase protein and most of its abnormal variants have now been identified. However, molecular genetic techniques such as polymerase chain reaction (PCR) amplification with allele-specific oligonucleotide probes for identifying abnormal pseudocholinesterase genotypes presently are available only in a limited number of research laboratories and are not in routine clinical use.

Histologic Findings

No characteristic alteration in liver histology is associated with genetic mutations in pseudocholinesterase enzyme synthesis.

TREATMENT

Section 6 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

Medical Care

• Pseudocholinesterase deficiency is a clinically silent condition in individuals who are not exposed to exogenous sources of choline esters.
• Patients with prolonged paralysis following administration of succinylcholine can be treated in the following ways:
• • Prophylactic transfusion of fresh frozen plasma can augment the patient's endogenous plasma pseudocholinesterase activity. This practice is not recommended because of the risk of iatrogenic viral infectious complications. However, perioperative transfusion of fresh frozen plasma administered to correct a coagulopathy may mask an underlying pseudocholinesterase deficiency.
  • Mechanical ventilatory support is the mainstay of treatment until respiratory muscle paralysis spontaneously resolves. Recovery eventually occurs as a result of passive diffusion of succinylcholine away from the neuromuscular junction.
  • Administration of cholinesterase inhibitors, such as neostigmine, is controversial for reversing succinylcholine-related apnea in patients who are pseudocholinesterase deficient. The effects may be transient, possibly followed by intensified neuromuscular blockade.

Consultations

• Consultation with a geneticist may help to identify the specific atypical genotype alleles contributing to pseudocholinesterase deficiency.
• Because the DNA sequence of the pseudocholinesterase gene and its amino acid structure is known, atypical alleles now can be identified by PCR amplification studies using DNA extracted from leukocytes in a blood sample.

FOLLOW-UP

Section 7 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

Complications

• The main complication resulting from pseudocholinesterase deficiency is the possibility of respiratory failure secondary to succinylcholine or mivacurium-induced neuromuscular paralysis.
• Individuals with pseudocholinesterase deficiency also may be at increased risk of toxic reactions, including sudden cardiac death, associated with recreational use of cocaine.

Prognosis

• Prognosis for recovery following administration of succinylcholine is excellent when medical support includes close monitoring and respiratory support measures.
• In nonmedical settings in which subjects with pseudocholinesterase deficiency are exposed to cocaine, sudden cardiac death can occur.

Patient Education

• Patients with known pseudocholinesterase deficiency may wear a medic-alert bracelet that will notify healthcare workers of increased risk from administration of succinylcholine.
• These patients also may notify others in their family who may be at risk for carrying one or more abnormal pseudocholinesterase gene alleles.

MISCELLANEOUS

Section 8 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Failure to take an adequate history of previous adverse reactions to succinylcholine, mivacurium, or cocaine in either the patient's own medical history or in the family history
• Failure to monitor skeletal muscle paralysis by electrical tetanic stimulation
• Failure to provide adequate respiratory function monitoring and support after the administration of succinylcholine or mivacurium

REFERENCES

Section 9 of 9

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• References

• Cerf C, Mesguish M, Gabriel I, et al. Screening patients with prolonged neuromuscular blockade after succinylcholine and mivacurium. Anesth Analg. Feb 2002;94(2):461-6, table of contents. [Medline].
• Cerf C, Mesguish M, Gabriel I, et al. Screening patients with prolonged neuromuscular blockade after succinylcholine and mivacurium. Anesth Analg. Feb 2002;94(2):461-6, table of contents. [Medline].
• Dietz AA, Rubinstein HM, Lubrano T. Colorimetric determination of serum cholinesterase and its genetic variants by the propionylthiocholine-dithiobis(nitrobenzoic acid)procedure. Clin Chem. Nov 1973;19(11):1309-13. [Medline].
• Jatlow P, Barash PG, Van Dyke C. Cocaine and succinylcholine sensitivity: a new caution. Anesth Analg. May-Jun 1979;58(3):- Van Dyke C. [Medline].
• Jensen FS, Viby-Mogensen J. Plasma cholinesterase and abnormal reaction to succinylcholine: twenty years'' experience with the Danish Cholinesterase Research Unit. Acta Anaesthesiol Scand. Feb 1995;39(2):150-6. [Medline].
• Kalow W, Genest K. A method for detection of atypical forms of human serum cholinesterase: Determination of dibucaine numbers. Can. J. Biochem. 1957;35:339.
• Lange D, du Pasquier Y. [Study of cellular immunity in the course of nephro-epithelioma. Preliminary study concerning 12 cases (author''s transl)]. J Urol Nephrol (Paris). Jul-Aug 1975;81(7-8):543-8. [Medline].
• Lehmann H, Liddell J, M - 196907. Human cholinesterase (pseudocholinesterase): genetic variants and their recognition. Br J Anaesth. Mar 1969;41(3):235-44. [Medline].
• Lovely MJ. Perioperative blood transfusion may conceal atypical pseudocholinesterase. Anesth Analg. 1990;70:326-327.
• Maiorana A, Roach RB. Heterozygous pseudocholinesterase deficiency: a case report and review of the literature. J Oral Maxillofac Surg. Jul 2003;61(7):845-7.
• Pantuck EJ. Plasma cholinesterase: gene and variations. Anesth Analg. 1993;77:380-386.

Article Last Updated: Jul 17, 2006