Phytosterolemia

A rare inherited disorder characterized by congenital hypercholesterolemia, presenting clinically with tendon xanthomas, premature coronary artery disease, and premature atherosclerosis.

Sitosterolemia.

First described in 1974 by Battacharyya and Connor in two sisters.

As of year 2000, in the United States approximately 50 patients have been identified. The incidence is suggested at 1:1,000,000 population. No ethnic predilection.

Autosomal recessive. The gene defect in sitosterolemia remains to be elucidated.

The nature of the primary defect is unknown at the molecular level, although enhanced intestinal absorption and reduced excretion of plant sterols appear to be the abnormality. Affected homozygote individuals show an enhanced absorption of both cholesterol and sitosterol from the diet, and decreased bile clearance of these sterols and their metabolites, resulting in markedly expanded whole-body cholesterol and sitosterol pools. Increased content of sitosterol in red cells may be responsible for the fragility of the RBCs and results in chronic hemolytic anemia.

Sitosterolemic homozygotes show elevation of plasma plant sterol (sitosterol and campesterol) concentrations.

Absorption of sitosterol in affected patients is 20 to 30%, as compared to 5% in normal individuals. The plasma concentrations of sitosterol in affected patients varies between 15 and 27% of the total sterol content and increased concentrations are found in cell membranes, xanthomas, and atherosclerotic plaques. Tendon and tuberous xanthomas developed at an early age, as with early development of atherosclerosis, and episodes of hemolysis and painful arthritis are features. Coronary atherosclerosis is common. Phytosterols can cause cholestasis in susceptible infants. Extramedullary sitosterolemic xanthomas have been reported to result in spinal cord compression. Episodic hemolysis and chronic hemolytic anemia may be present.

Detailed cardiovascular assessment. Where indicated, not only should the global ventricular function be assessed by echocardiography, but angiography with angioplasty may improve coronary flow prior to elective surgery. Elective surgery should be postponed until at least 6 months from any myocardial infarction. Current congestive heart failure also carries higher risk of another perioperative cardiac event. Obtain drug history (nitrates, beta blockers, calcium channel blockers, antiplatelet agents, digoxin). Patients with painful arthritis may be on long-term nonsteroidal anti-inflammatory drugs (NSAIDs). The signs and symptoms of anemia must be sought. Anemia is poorly tolerated in patients with coronary artery disease and every effort should be made to correct the deficit preoperatively. Investigations: cell blood count, ECG, chest radiograph, coagulation studies, and bleeding time if the patient is on antiplatelet agents and/or heparin. Premedication with adequate sedation to reduce anxiety, continue medical therapy, and administer oxygen therapy during transport to the operating theatre.

The conduct of anesthesia and the choice of monitors depend primarily on the underlying cardiac status of the patient, and the type and extent of the proposed surgery. Aim to maintain optimal myocardial oxygen supply-demand balance (avoid hypoxemia, sympathetic stimulation, pain, and tachycardia). A central neuraxial block (spinal, epidural) is relatively contraindicated in those patients on aspirin or other antiplatelet agents.

Considerations must be given to the effects of the anesthetic medications and the cardiovascular problems.

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