Differentiation of Non-Polio Acute Viral Myelitis Is Mandatory for Polio Eradication in China

The global poliomyelitis eradication initiated by WHO in 1988 has prompted China to declare that polio will be eradicated in that country by the year 2000. A gradual increase in the number of children with polio culminated in the latter part of 1980s in major outbreaks, and reported polio cases reached ∼10 000 during 1989 through 1990.1 However, because of intense national immunization programs, together with strengthened Expanded Programme on Immunization activities, indigenous wild polio virus has not been isolated since 1995. Accordingly there has been a drastic decrease in the number of newly affected children, although a few imported cases were identified along border zones with southeastern Asian countries during 1996 and 1997. Since acute flaccid paralysis (AFP) defined by the WHO includes diverse paralytic childhood diseases, the differentiation of polio from other disorders giving rise to AFP has been imposed on us for neurologic assessment. The Chinese paralytic syndrome reported in 1991,2 the clinical manifestation of which differed from classical Guillain-Barré syndrome (GBS) and was difficult to distinguish from polio, was later concluded to be an acute axonal form of GBS triggered by Campylobacter jejuni enteritis. While engaged in the clinical surveillance of poliomyelitis in China since 1990, we have repeatedly recognized another entity of AFP, which has created a particular challenge for us in terms of etiologic diagnosis. In particular this involved a group of children who developed non-polio acute viral myelitis. When poliomyelitis was prevalent in the early part of the 1990s, this did not appear to be a major problem, because most AFP cases other than GBS were poliomyelitis. However, when the incidence of polio was greatly reduced in 1995, it became our task to distinguish clinically between definite polio cases and those with non-polio acute myelitis of presumable viral cause. This has been our major concern since our clinical surveillance shifted from Shandong Province to the four southern provinces, where a large population of minority races reside in mountainous areas and on border zones with southeastern countries. During the latter part of 1997 we performed neurologic examinations on a total of 92 children with AFP in three provinces of China (Shanzi 8, Guizhou 42 and Yunnan 42 cases) to assess polio-compatible cases among those with AFP of diverse causes (Table 1). Virus recovery was attempted from stool specimens. Nine of 92 cases were clinically diagnosed as having poliomyelitis, although no wild type polio strain was isolated. The viral antibody titers of the individual cases were not evaluated, however.TABLE 1: Clinical diagnosis of acute flaccid paralysis, Shanxi, Guizhou and Yunnan Province There were 19 patients whose clinical diagnosis was nonpolio acute viral myelitis. Among them, poliovirus was isolated in 6 cases and enterovirus species in 5 (Table 2). Those cases with non-polio acute viral myelitis were characterized by a constellation of symptoms and signs that were difficult to distinguish from acute paralytic poliomyelitis. Among 21 cases thought to have polio 9 were shown to have non-polio acute viral myelitis. A moderate to high febrile state, lasting for several days, was followed by rather asymmetric and often segmental paralysis and muscle atrophy of the lower limb(s). Notable was the demonstration of abolished or depressed muscle stretch reflexes involving the affected muscles, whereas exaggerated reflexes were prominent features in other muscle segments. Crossed adductor response, a manifestation of impaired corticospinal innervation, was often demonstrated. Plantar response was also frequently extensor although in infants it may have been physiologic. Ankle clonus, which is pathognomonic of upper motor involvement, was occasionally demonstrated in this group. Sensory findings and bladder dysfunction, if present, were difficult to ascertain in small children.TABLE 2: Virus isolation from stool specimens in final clinical diagnosis This paralysis, apart from often subtle upper motor signs, is quite similar to that seen in poliomyelitis. In contrast spastic paraplegia, a hallmark of transverse myelitis, is not usual. Transverse myelitis, a closely related differential category, is characterized by acute onset paraplegia of diverse causes,3 and clinical differentiation from polio is not difficult. However, the cases we have described are not transverse lesions in the spinal cord. The lower motor system is involved in an asymmetric manner, and often a unilaterally prominent longitudinal lesion was likely along the anterior horn, together with extension of the process into the adjacent white matter. The non-polio acute viral myelitis described here is not listed in WHO as a differentiation of AFP. This particular polio-like acute myelitis has been reported in association with several enterovirus infections in childhood. As seen in the Table 2, viral recovery is not a useful approach, given that vaccine strains have been isolated often from this group as well as from GBS and clinical compatible polio cases. Also, non-polio enteroviruses have been similarly recovered in those three major groups. Accordingly an awareness of this group of AFP is important in this region of China, because it is highly likely that it is considered as polio. The quality of attenuated vaccines produced in China has been suspected of being less than optimal quality, given that the incidence of vaccine-related paralysis appears high. However, from our surveillance there is another probable explanation because these cases of non-polio acute viral myelitis may have been included in the polio statistics. It is not certain whether the incidence of this form of myelitis is more prevalent in southern China. However, it is our impression that these enterovirus species appear more indigenous to southern than to northeastern China. The eradication of polio in China has been progressing successfully. The awareness of non-polio acute viral myelitis of the nontransverse type, which is likely caused by a non-polio enterovirus infection of the spinal cord, is of increasing importance as polio eradication reaches its final stage toward the year 2000. Choichi Hida, M.D. Teiji Yamamoto, M.D. Yasuo Chiba, M.D. Yu Jingjin, M.D.