This syndrome is the result of weakness or paralysis of muscles that are supplied by the motor nuclei of the lower brainstem, that is, the motor nuclei of the fifth, seventh, and ninth to twelfth cranial nerves. (Strictly speaking, the motor nuclei of the fifth and seventh nerves lie outside the “bulb,” which is the old name for the medulla oblongata.) Involved are the muscles of the jaw and face; the sternocleidomastoids and upper parts of the trapezii; and the muscles of the tongue, pharynx, and larynx. If weakness develops rapidly, as may happen in GBS, diphtheria, or poliomyelitis, there is no time for muscle atrophy. Myasthenia gravis, inclusion body myopathy, and polymyositis on rare occasions may produce such a picture, but motor neuron disease is the most common cause. When the latter disease is isolated to the bulbar muscles, it has been called progressive bulbar palsy, as discussed in Chap. 38. This can also be a presentation of Kennedy bulbospinal atrophy. The chronic forms of motor neuron disease and the childhood form of Fazio-Londe disease result in marked wasting and fasciculation of the facial, tongue, sternocleidomastoid, and trapezius muscles. All of these disorders must be differentiated from pseudobulbar palsy that is discussed in Chaps. 24 and 25.
As one can readily understand, several cranial nerves may be affected by a single disease process. The first clinical problem that arises is whether the lesion lies within or outside the brainstem. Lesions lying on the surface of the brainstem, infiltrating the meninges, or situated at the base of the skull are characterized by involvement of adjacent cranial nerves (often occurring in succession) and by late and only slight, if any, involvement of the long sensory and motor pathways. These syndromes are discussed later and listed in Table 44-1 by their eponymic designations. The opposite is true of intramedullary, intrapontine, and intramesencephalic lesions; within the brainstem that involve cranial nerves and produce crossed sensory or motor paralysis (cranial nerve signs on one side of the body and tract signs on the opposite side, the historical aspects of which are reviewed by Silverman et al). In this way, a number of distinctive brainstem syndromes, to which eponyms have also been attached, are produced; these are listed in Table 33-5 because they are most often the result of brainstem stroke. The special problems of multiple cranial nerve palsies of the ocular motor nerves are addressed in Chap. 13.
Involvement of multiple cranial nerves outside the brainstem may be the result of trauma; localized infections such as herpes zoster (subacute onset); Lyme disease as reported by Schmutzhard and colleagues; cytomegalovirus (CMV) infection in an HIV patient; Wegener granulomatosis, sarcoidosis, other types of granulomatous diseases, or compression by tumors and saccular aneurysms. The sequential painless affection of contiguous or noncontiguous nerves over several days or weeks is particularly characteristic of meningeal carcinomatosis or lymphomatosis. In the series of 79 cases accumulated by Keane (2005), tumor was by far the most common underlying cause of multiple cranial nerve palsies— particularly schwannomas, metastases, and meningiomas; trauma, infection, and vascular disease followed in frequency after neoplasm. The eighth nerve is commonly incorporated in these neoplastic meningeal infiltrations. Among the solid tumors that cause local compression of nerves, neurofibromas, schwannomas, meningiomas, cholesteatomas, carcinomas, chordomas, and chondromas have all been observed. Nasopharyngeal carcinoma (Schmincke tumor or lymphoepithelioma) may implicate several cranial nerves in succession by invading the base of the skull (mainly the fifth and sixth but also higher nerves;