A Third Arm on the Chest: Implications for the Cortical Reorganization Theory of Phantom Limbs

A 31-year-old woman noticed unusual thirst and was diagnosed with SjS by a salivary gland biopsy. At age 46, she developed a sudden right hemiparesis. An oval lesion was detected in the left internal capsule by MRI. At age 51, she developed sudden paraplegia, which resolved over a week. However, 3 weeks later she developed tetraplegia and total anesthesia below the C4 level. She was then admitted to our hospital.

On admission, she was alert and not demented or aphasic, but she was anosognosic and frequently denied her paresis. Her cranial nerves were intact. She showed a near total tetraplegia and total anesthesia below the C4 level. Brain MRI scans revealed multiple oval lesions in the deep white matter, bilateral thalamus, bilateral basal ganglia, and left internal capsule. Spinal cord MRI scans revealed a lesion extending from C1 to Th12, most prominently over the C4 to Th1 region.

During our observation period, she claimed to have the sensation of an extra arm arising from the middle of her upper chest. She explained that it was painless and of the same length as her real arms. She claimed that she was able to move the extra arm. She and her husband reported that the phenomenon occurred after the episode of tetraplegia. This phenomenon continued for 14 months after her admission.

In addition to intra-oral desiccation and xerotic keratoconjunctivitis, SjS occasionally causes various neurological symptoms. We made a diagnosis of SjS with central nervous system symptoms.⁵ To our knowledge, this is the first report of a phantom limb in the context of SjS.

The cortical reorganization theory would provide the most plausible explanation for her phantom limb.^1,2 The cortical topography of somatic sensations is being constantly updated in response to various sensory inputs. Because the upper chest area is bordered by the shoulder/arm area on the somatosensory “homunculus,” it can be supposed that her deafferentated somatosensory areas that previously represented the shoulder/arm begin to receive the intact input from the intact sensory neurons of the upper chest. Interestingly, the midline of our trunk is redundantly represented by bilateral somatosensory areas. This double representation would have caused any sensory input from her upper midline chest area to arrive not only at the somatosensory upper chest area but also at the right and left shoulder/arm areas simultaneously. The repeated coincidence of such inputs into the bilateral shoulder/arm somatosensory areas may have provoked a feeling of two arms amalgamating into one, creating the sensation of the supernumerary arm on the chest. In addition, her anosognosic tendencies due to her cortical and subcortical lesions may have allowed the extraordinary belief of having three arms.