see rod myopathy

[MIM 609 284, 609 285]

(Cap myopathy)

Very rare. Congenital myopathy (autosomal dominant transmission) close to the rod myopathy (nemaline rod myopathy). It may be caused by a mutation of:

-         TPM2 gene (9p13.3)  coding for the β-tropomyosin in the slow type I striated muscle fibers [MIM 609 284]

-         TPM3 gene (1q21.3) coding for the α-tropomyosin in the slow type I striated muscle fibers [MIM 609 285]

-         ACTA-1 gene (1q42.13) coding for actin

The tropomyosin binds to actin to regulate muscle contraction.

The typical histological picture is the presence of eosinophilic and basophilic structures resembling small caps ("cap") on the periphery of muscle cells, under the sarcolemma: they are actually clusters of myofibrils and actin with expanded Z disks and without large filaments. These caps sometimes look like the sticks (rods) seen in nemaline rod myopathy. There is often a hypotrophy or a predominance of type I fibers. The severity of the affection seems to be related to the proportion of affected fibres: 70-75 % in the rapidly fatal neonatal form compared with 20-30 % in the more stable infantile form.

Clinical signs: hypotonia mainly at the level of the proximal and neck muscles, arched palate, myopathic facies, progressive respiratory insufficiency. Occasionally: micrognathia, scoliosis. CPK level: normal or low.

Anesthetic implications: 

tropomyosin dysfunction causes dysfunction of the receptor to the ryanodine receptor. In addition, given the possibility of a phenotypic continuum with congenital myopathies at risk of malignant hyperthermia (core myopathy, nemaline rod myopathy, congenital disproportion of muscle fibers), these patients should be considered as susceptible to malignant hyperthermia. 

Risk of difficult intubation. Muscular atrophy and swallowing disorders.

References : 

-         Goebel HH. 
Cap disease uncapped. 
Neuromusc Disord 2007; 17: 429-32

-         Maues De Paula A, Franques J, Fernandez C, Monnier N et al. 
A TPM3 mutation causing cap myopathy. 
Neuromusc Disord 2009; 19: 685-8

-         Tajshargi H, Ohlsson M, Lindberg C, Oldfors A. 
Congenital myopathy with nemaline rods and cap structures caused by mutation in the β-tropomyosin gene (TPM2). 
Arch Neurol 2007; 64: 1334-8.

-         Shenkman Z, Sheffer O, Erez I, Litmanovic I, Jedeikin R. 
Spinal anesthesia for gastrostomy in an infant with nemaline myopathy. 
Anesth Analg 2000; 91: 858-9.

-         Klingler W, Rueffert H, Lehmann-Horn F, Girard T, Hopkins PM. 
Core myopathies and risk of malignant hyperthermia. 
Anesth Analg 2009; 109: 1167-73.

-         Brislin RP, Theroux MC. 
Core myopathies and malignant hyperthermia susceptibility : a review. 
Pediatr Anesth 2013 ; 23 : 834-41.

-        North K, Wang C, Clarke N, Jungbluth H, Vainzof M, Dowling J et al. 
Approach to the diagnosis of congenital myopathies. 
Neuromuscul Disord 2014 ; 24 : 97-116.  

-        Benarroch L, Bonne G, Rivier F, Hamroun D.
The 2020 version of the gene table of neuromuscular disorders.
Neuromusc Dis 2019 ; 29 : 980-1018 ou  http://www.musclegenetable.fr.

Updated: June 2021