It is a genetic disorder characterized by distal, late-onset myopathy. The presenting feature is in 89% of cases weakness and wasting of the small long extensor muscles of the hands and feet. Myotonia and sensory changes are not present. It gradually affects the distal muscles of the lower extremities. The association between this disorder and heart problems is not as frequent as it is the case with congenital myopathies. However, cardiomyopathic cases have been reported.
Swedish Distal Myopathy Type; Welander Muscular Atrophy.
Welander distal myopathy is observed almost exclusively in Sweden, where it was first described; more than 250 cases have been described.
Autosomal dominant inheritance. The gene causing Welander myopathy has not yet been identified, but is restricted to a region of 2.4 cM on chromosome 2 (2p13).
Unknown, but the gene locus region overlaps with those of Miyoshi myopathy and limb-girdle muscular dystrophy IIB, both of which result from mutation in the dysferlin gene.
Levels of creatine kinase are normal to slightly increased. The most prominent finding on light microscopy is that of rimmed vacuoles and tubulofilamentous inclusions evidenced by ultrastructural examination.
Distal myopathy with late onset (after age 40 years). The first symptom is clumsiness in performing fine motor skills with the index finger and thumb. The weakness subsequently progresses to all the finger extensor muscles, and atrophy of intrinsic hand muscles becomes manifest after several years’ duration. The weakness later extends to the anterior muscles of the legs with inability to raise the forefoot appropriately. No proximal weakness and no cardiomyopathy. Progression is slow and does not affect life expectancy.
Precautions before anesthesia
It is important to obtain baseline serum potassium and creatine kinase (CK) concentrations to assess muscle membrane integrity. Also, a family history, information about previous anesthetic and medical problems, cardiac function test and other underlying medical conditions features must be sought. It is possible that high baseline values may be associated with increased risk of profound perioperative rhabdomyolysis, whereas the baseline value per se is required to differentiate perioperative rhabdomyolysis from preexisting muscle damage. Obtain complete laboratory workup and neurologic evaluation. Cardiac function should be assessed in light of cardiomyopathic potential of other distal myopathy. ECG, echocardiography, and/or cardiac catheterization may be appropriate. Other syndromic features should be sought. If regional anesthesia is planned, a preoperative assessment of peripheral sensory nerve dysfunction should be considered. Increased sensitivity to respiratory-depressant drugs should be anticipated and even with the most careful anesthesia management, postoperative ventilatory support may be required and intensive care availability should be checked before any elective surgical procedure, even minor.