A six-year-old, male, neutered Cocker spaniel was referred for a three-week history of progressive thoracic limb stiffness. The dog became non-ambulatory due to severe thoracic limb stiffness, which was exacerbated by external stimuli. The pelvic limbs appeared to be normal. Based on the history and the physical examination, a presumptive diagnosis of focal tetanus of the thoracic limbs was made. The dog was treated supportively with tetanus antitoxin, antimicrobials, sedation and muscle relaxants; however, this treatment did not control the muscle spasms adequately. Magnesium sulphate was added to alleviate the muscle spasms and to reduce the sedation requirements. The dog improved and was discharged after three weeks of intensive treatment.