The most frequent neural complications of the myeloma are those referable to the spinal cord and roots. The almost constant involvement of the spinal vertebrae in this disorder readily explains the neural manifestations. The pressure exerted by the invading neoplasm on the spinal cord or by the diseased vertebrae on the vessels of the spinal cord leads to a myelopathic process, thus interfering with the normal conduction of neural impulses of the various fiber tracts. The occurrence of root pains, herpes zoster or peripheral neuritis is the end-result of direct pressure on the roots of the spinal cord, the spinal ganglions and the peripheral nerves. Although metastases to the bones of the skull are frequent, mental symptoms and other signs of cerebral involvement are rarely observed. Compression of the cerebral structures by the metastases to the skull, apparently, is not sufficient to elicit neurologic symptoms.
The rarity of the disease
DAVISON C, BALSER BH. MYELOMA AND ITS NEURAL COMPLICATIONS. Arch Surg. 1937;35(5):913-936. doi:10.1001/archsurg.1937.01190170082008