Mitochondrial Myopathy

More common than previously thought. Prevalence ranges from 1:7000–15,000.

Occurrence is usually sporadic or maternally inherited.

Metabolic acidosis

Respiratory and cardiac insufficiency/failure

Delayed emergence

Respiratory failure following sedation.

Consider aspiration risk.

Metabolic acidosis.

Hypotension during induction.

Clinically heterogeneous collection of diseases with myopathy of mitochondrial origin as common trait. Defects can be in electron transport, fatty acid, and amino acid metabolism.

Commonly associated with encephalopathy.

Nomenclature rapidly changing to reflect discovery of specific genetic mutations. The following all are mitochondria-based disorders that may include a myopathic component: Kearns-Sayre syndrome (KSS); Pearson syndrome (PS); maternally inherited Leigh syndrome (MILS); late-onset Leigh syndrome; mitochondrial encephalomyopathy, lactic acidosis, and stroke-like symptoms (MELAS); myoclonic epilepsy with ragged red fibers (MERRF); Leber hereditary optic neuropathy (LHON); chronic progressive external ophthalmoplegia (CPEO); and neuropathy, ataxia, and retinitis pigmentosa (NARP).

Onset is variable. Most severe phenotypes present in infancy.

Most common symptom is muscle weakness, and most common sign is lactic acidosis, resulting from the inefficient metabolism of pyruvate and shift to anaerobic respiration.

Muscle biopsy often used for suspected cases. Hallmark is appearance of ragged red fibers.

Biochemical analysis of mitochondria often needed to make exact diagnosis.

Anesthetic sensitivity may manifest as decreased MAC of inhaled anesthetics (e.g., complex I disorders), increased respiratory insufficiency from sedatives and narcotics, and decreased hepatic clearance or renal excretion of IV agents.

Genetic variation in either mtDNA or nDNA.

Large-scale mtDNA deletions (e.g., KSS, PS, PEO) are most often acquired sporadically.

Single-base mtDNA changes (e.g., MELAS, MERRF, MILS, LHON) are often inherited maternally and usually affect mitochondrial protein synthesis (via mRNA, tRNA, or rRNA) or components of the electron-transport chain (i.e., complex I, III, IV, V).

Single-base nDNA changes (e.g., late-onset Leigh syndrome) are often inherited in mendelian patterns (autosomal dominant or recessive).