Multicore Myopathy

At a glance

It is a congenital muscular disease characterized by the presence of generalized and progressive muscle weakness. Other features include cardiac considerations such as congestive, hypertrophic, or restrictive cardiomyopathy. The onset of muscle hypotonia begins in infancy and is often described as the “floppy baby.” It is usually affecting mainly the proximal musculature leading to decreased muscle bulk. Ptosis and oculomotor palsy are sometimes observed.

Synonym

Minicore Myopathy.

Incidence

Rare; 80 cases have been described.

Genetic inheritance

Most cases seem sporadic, but an autosomal recessive inheritance pattern is sometimes found.

Pathophysiology

Accumulation of desmin in both skeletal muscle and myocardium.

Diagnosis

Muscular biopsy shows increased variation in fiber size and a predominance of type 1 fibers. Multiple circumscribed small lesions (cores) are seen within each involved fiber. Both type 1 and type 2 fibers are affected. Histologically, the cores of the muscles are areas characterized by loss and/or disorganization of the myofibrillar structure and by absence or severe reduction of mitochondria.

Clinical aspects

Muscular weakness is generally mild and nonprogressive, but cardiac involvement has been described in some patients. The cardiomyopathy can be congestive, hypertrophic, or restrictive, sometimes requiring cardiac transplantation. Muscle weakness that begins in infancy (“floppy baby”) is usually proximal, with hypotonia and decreased muscle bulk. Ptosis and oculomotor palsy are sometimes observed. Motor development is delayed, but intelligence is normal. Diaphragmatic involvement can lead to hypoventilation during sleep.

Precautions before anesthesia

As in any child presenting with a muscular disorder, thorough cardiac evaluation (ECG, echocardiography) is mandatory; respiratory involvement should be assessed both in the awake and the sleeping state (polysomnography). For elective surgical procedure, it is recommended to obtain an anesthesiology consultation.

Anesthetic considerations

By analogy with central core disease, malignant hyperthermia-triggering agents should be avoided in these patients. One case of unexplained fever and death has been described in a 30-month-old boy with this disease a few hours after cardiac catheterization with meperidine, hydroxyzine, and intravenous ketamine.

Pharmacological implications

Careful titration of nondepolarizing muscle relaxants if needed; succinylcholine should be avoided for fear of rhabdomyolysis and hyperkalemia or even malignant hyperthermia crisis.

Other condition to be considered

• Zaspopathy (ZASP-related Myofibril Myopathy): It is a novel medical condition that was first described in 2005 that is characterized by the late onset of a progressive muscular dystrophy associated with the presence of dysfunctional myofibril in the actin component. It is inherited as autosomal dominant. The clinical features include multiple forms of both distal and proximal myopathies. It ...