Multicore Myopathy

Congenital muscular disease. Muscle weakness is generally mild and nonprogressive. Cardiac involvement has been described; the cardiomyopathy can be congestive, hypertrophic, or restrictive. Muscle hypotonia begins in infancy (“floppy baby”) and is usually affecting mainly the proximal musculature leading to decreased muscle bulk. Ptosis and oculomotor palsy are sometimes observed.

Minicore Myopathy.

Rare; 80 cases have been described.

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

Accumulation of desmin in both skeletal muscle and myocardium.

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 core of the muscles are areas characterized by loss and/or disorganization of the myofibrillar structure and by absence or severe reduction of mitochondria.

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.

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.

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.

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