Clinical History
The dog presented with a recent history of muscle tremor, reluctance to exercise and collapse upon walking only a few steps.

Physical and Neurological Examination
When walking, the dog was very tentative on his pelvic limbs with a crouched stance (Go to video clip).  Generalized muscle atrophy was evident most notably in the pelvic limbs. Neurological examination was within normal limits and no pain was elicited upon palpation of the vertebral column.  All other clinical parameters including heart rate and body temperature were within normal limits. Given the age, breed and clinical signs, “central core” like myopathy of Great Danes, another myopathy, or possibly a cervical spondylopathy were considered.

Diagnostic Testing

CBC: Unremarkable

Serum Chemistry: Creatine kinase was elevated at 1519 IU/L (reference 75-230) and total protein was mildly decreased at 56.1 g/l (reference 63-71)

Radiographs of cervical spine: Within normal limits

Electrophysiology: Electromyography revealed fibrillation potentials in the quadriceps muscle group, triceps, gluteal and hamstring muscles. The motor nerve conduction velocity was 42.9 m/sec.

Muscle and nerve biopsies: Fresh and fixed specimens were collected from the quadriceps and triceps muscles, and the common peroneal nerve. The predominant pathological change within both muscle biopsies was the presence of large central zones that were basophilic on H&E staining (Fig. 1A) and darkly stained with the oxidative reactions SDH (Fig. 1B) and cytochrome C oxidase (not shown). No abnormalities were identified within resin embedded peripheral nerve sections.

Fig. 1A. H&E stain frozen muscle biopsy

Fig. 1B. SDH reaction

Diagnosis and Outcome
Non-inflammatory myopathy with cytoarchitectural changes consistent with the “Central Core” myopathy previously described by Targett et al in an 8 month old female Great Dane. In a review of the data base of the Comparative Neuromuscular Laboratory, 5 Great Dane dogs all from the UK were previously diagnosed with this disorder (Shelton, personal communication). Onset of clinical signs was from 6-8 months of age with progressive muscle wasting (Fig. 2), exercise intolerance, generalized body tremors, and collapse. All cases showed the typical central cytoarchitectural changes. The dog of this report was euthanized because of progressive deterioration and no specific therapy available. Since this dog was diagnosed, 2 other puppies from the same litter were found to be affected.

Figure 2. Great Dane puppy with "core-like" myopathy

It is important not to confuse this disorder with Central Core Disease described in humans. Histochemical stainings of muscle biopsies from human patients show important differences from that of the Great Dane dogs. Core-like structures stain intensely with oxidative enzymes in the dogs but are unstained in muscles from human patients. EM studies by Targett et al described accumulations of normal appearing mitochondria and glycogen within the cores, which are also absent in human patients. More work clearly needs to be performed to better characterize this interesting myopathy.

References

Targett MP, Franklin RJM, Olby NJ, Dyce J, Anderson JR, Houlton JEF. Central core myopathy in a great dane. J Small Anim Pract 35:100-103, 1994.

Fardeau M, Tome’ FMS. Congenital Myopathies. In : Myology (Engel AG, Franzini-Armstron C eds). McGraw-Hill, New York 1994, pp 1487-1532.