Background: Diagnosis of consciousness can be very challenging in some clinical situations such as severe sensory-motor impairments. Case study: We report the case study of a patient who presented a total “locked-in syndrome” associated with and a multi-sensory deafferentation (visual, auditory and tactile modalities) following a protuberantial infarction. Result: In spite of this severe and extreme disconnection from the external world, we could detect reliable evidence of consciousness using a multivariate analysis of his high-density resting state electroencephalogram. This EEG-based diagnosis was eventually confirmed by the clinical evolution of the patient. Conclusion: This approach illustrates the potential importance of functional brain-imaging data to improve diagnosis of consciousness and of cognitive abilities in critical situations in which the behavioral channel is compromised such as deafferented locked-in syndrome.