A 20-year-old male patient presented with myalgia of upper limbs and myasthenia of extremities for more than 1 month. Physical examination showed diffuse erythema on the cheeks, upper eyelids, upper chest, neck and dorsa of the hands. The myodynamia of the proximal and distal muscles of upper and lower extremities was grade Ⅳ, Ⅴ, Ⅲ and Ⅴ respectively. Laboratory examinations revealed that the serum levels of creatine kinase, CK-MB and lactate dehydrogenase were 2103 U/L, 83 U/L and 489 U/L respectively, which were all above the normal range. Electromyogram revealed myopathic abnormality and normal nerve conduction velocity. Histopathology of gastrocnemius muscle showed hypertrophy and swelling of muscle fibers, disappearance or fuzziness of transverse striation, and intermuscular lymphoid cell infiltration. A biopsy of the skin lesion from the upper chest showed liquefaction degeneration of and colloid bodies in basal cell layer, perivascular lymphoid cell infiltration in the dermis. A diagnosis of dermatomyositis was established based on the clinical and laboratory findings. After management with intravenous prednisolone 80 mg once daily and symptomatic treatment for 4 weeks, the myodynamia of upper limbs was improved, serum levels of creatine kinase,CK-MB and lactate dehydrogenase reached the normal ranges. However, the myodynamia of lower limbs progressively deteriorated with the emergence of paresthesia. Enhanced MRI scan showed a tumor in the vertebral canal at the level of thoracic vertebra 11 to 12. A spherical encapsulated tumor measuring 3 cm in diameter was surgically removed. The tumor was diagnosed as paraganglioma in vertebral canal according to pathological and immunohistochemical findings. The patient was finally diagnosed with paraganglioma in vertebral canal superimposed on dermatomyositis.