RESUMEN
INTRODUCTION: Myositis of unknown aetiology might be a very rare complication of intramuscular injections of onabotulinum toxin A (Botox) for spasticity treatment. CASE PRESENTATION: We describe a case of significant myositis of unknown aetiology in a 17-year-old man, who was admitted for rehabilitation 4 months after his initial spinal cord injury (SCI) as a result of a mountain bike accident. He has an incomplete tetraplegia, C4 AIS B international Standards for Neurological Classification for Spinal Cord Injury (ISNCSCI) [1] due to C5 vertebra 3 column fracture [2]. He had severe spasticity of his lower limb muscles treated with Botox, following which, he required two acute hospital transfers for diagnosis and management of myositis. DISCUSSION: This is a severe unusual presentation of myositis caused by intramuscular botulinum toxin for treatment of spasticity, in the frequent setting of spasticity where intramuscular botulinum toxin injections are routinely used.