Supernumerary phantom limbs in spinal cord injury

Case report and review of supernumerary phantom limbs in patients suffering from spinal cord injury (SCI).

SCI rehabilitation centre.

After a ski accident, a 71-year-old man suffered an incomplete SCI (level C3; AIS C, central cord syndrome), with a C3/C4 dislocation fracture. From the first week after injury, he experienced a phantom duplication of both upper limbs that lasted for 7 months. The supernumerary limbs were only occasionally related to painful sensation, specifically when they were perceived as crossed on his trunk. Although the painful sensations were responsive to pain medication, the presence of the illusory limb sensations were persistent. During neurological recovery, the supernumerary limbs gradually disappeared. A rubber hand illusion paradigm was used twice during recovery to monitor the patient's ability to integrate visual, tactile and proprioceptive stimuli.

Overall, the clinical relevance of supernumerary phantom limbs is not clear, specific treatment protocols have not yet been developed, and the underlying neural mechanisms are not fully understood. Supernumerary phantom limbs have been previously reported in patients with (sub)cortical lesions, but might be rather undocumented in patients suffering from traumatic SCI. For the appropriate diagnosis and treatment after SCI, supernumerary phantoms should be distinguished from other phantom sensations and pain syndromes after SCI.