Congenital Myotonia in 2 Domestic Cats

Abstract

ongenital myotonia was diagnosed in a male and a C female domestic cat. Physical examination revealed gait abnormalities and marked nonpainful enlargement of proximal appendicular muscles in both cats. A myotonic dimple was evoked in 1 cat. Thyrotropin-releasing hormone response testing was normal in 1 cat, and the adrenocorticotropic hormone response was normal in the other. Electromyography revealed classical myotonic discharges. Muscle biopsies from both cats were characterized by moderate hypertrophy by light microscopy and revealed mild dilatation of transverse-tubules by electron microscopy. Immunoblotting and immunostaining of muscle tissue were positive for the presence of dystrophin. Specific treatment was not attempted in either case. This is the first description of congenital myotonia in the domestic cat. Case DescriptionsTwo young sibling domestic cats were presented to the Companion Animal Hospital of the New York State College of Veterinary Medicine (NYSCVM) for evaluation. Cat 1 was a 5-month-old intact male Domestic Shorthair cat with the presenting complaint of hind limb weakness and occasional falling over; cat 2 was a 9-month-old intact female Domestic Longhair cat with a presenting complaint of clumsiness, stiff gait, and falling over. Cat 2 had been seen previously at 4 months of age and was diagnosed with a presumptive myopathy; further diagnostic evaluation had been declined at that time and the clinical signs had remained unchanged. Physical examinations in both cats revealed unthrifty animals with a crouched hind limb stance and profound enlargement of proximal appendicular muscles; the tongue of cat 1 was moderately enlarged. No pain, asymmetry, or fever were noted. Both cats exhibited a short-strided, choppy gait, which appeared to improve with exercise in cat 1. Cat 2 had prolonged blepharospasm in response to digital stimulation of the palpebral fissures, and prolonged facial distortion after meowing or hissing. Both cats could vocalize only weakly and cat 1 would occasionally developed transient respiratory stridor and cyanosis when stressed during handling. Results of complete ophthalmologic and neurologic examinations were normal.Results of a CBC and serum biochemical profile including creatine kinase activity were within normal limits (Table 1); similar results were obtained when Cat 2 was originally evaluated. An enzyme-linked immunosorbent assay for feline leukemia virus and serum immunoglobulin G (IgG) titers for Toxoplusma gondii were negative in both cats. Survey radiography of the thoracic and pelvic limbs of cat 1 were normal. Electrocardiography and echocardiography were normal in cat 1; echocardiography revealed mild enlargement of the left atrium and pulmonary trunk, and scant pinpoint hyperechoic foci in the left ventricular endocardium of cat 2, a5 well as subjective rounding of the 0.37 ng/mL, reference range = 0.3-0.9 ng/mL; baseline T, = 1.10 pg/dL, reference range = 1.5-4.0 pg/dL; post-TRH T, = 1.00 ng/mL, reference range = 0.3-2.0 ng/mL; and post-TRH T, = 2.30 p...

A Novel Mutation in CLCN1 Associated with Feline Myotonia Congenita

“…Variable findings have been described for both light and electron microscopy in feline MC, including occasional degeneration of individual myofibers associated with localized proliferation of sarcolemmal nuclei with few centrally located nuclei, moderate diffuse myofibril hypertrophy, rounding of the sarcoplasm, clear cytoplasmic vacuoles within many myofibers and mild dilatation of transverse T-tubules [27]–[29]. The mean myofiber perimeter and areas were previously measured and compared to age-matched controls using image software, showing increased perimeters and areas of myofibers in affected cats [27], [28]. The muscle profiles in this study showed hypertrophy of both type 1 and type 2 fibers with a normal mosaic pattern of muscle fiber types and no evidence of inflammation, necrosis, fibrosis or other specific cytoarchitectural abnormalities, consistent with a diagnosis of MC.…”

“…In goats, MC is inherited as an autosomal dominant trait [22]. Since the first description of caprine MC [23], historical, clinical, electrodiagnostic and histopathologic features have become well-established in horse [24], dog [25], [26] and cat models [27]–[30]. In the feline model, historical and clinical findings, along with routine blood testing, muscle percussion, cardiac examination, electrodiagnostic testing and muscle histopathology have been characterized in two related kittens and in four kittens from separate litters [21], [23].…”

Classification of Involuntary Movements in Dogs: Myoclonus and Myotonia

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Congenital diseases of feline muscle and neuromuscular junction

“…Myotonia is the continued active contraction of a muscle after the cessation of voluntary effort and is characterised by muscle spasm and stiffness (Braund, 1986). Hereditary myotonia has been reported in a variety of species but only recently in the cat (Hickford et al, 1998;Toll et al, 1998). Myotonia can occur secondary to other disorders; muscular dystrophies and endocrinopathies or as a primary disorder; myotonia congenita.…”