Page 135 - Read Online

Modified osserman classification is also commonly used ocular muscle involvements, and generalization
to distinguish subtype of MG patients and indicates of symptoms occur in only 44% of patients within
the different prognosis and treatment response. This 2 years. [37] In a follow‑up study including 96 Thai
classification has been frequently recommended and patients with ocular MG, only 15 patients (15.6%)
widely used over the past several decades in China. developed generalized symptoms within 2 years from
Although the modified Osserman classification is based the initial diagnosis. [38] It is to be noted that about
on clinical symptoms, impact on work and daily life, 50% of Chinese MG patients present with pure ocular
course of disease and treatment response, it is extremely manifestations during their entire lifetime, with a
[5]
challenging to take into account the prognosis and relatively lower rate of generalization. Recently, Jing
disability of patients. Moreover, this classification et al. [39] have also reported that only 26% of Chinese
does not contain MG‑associated auto‑antibodies and patients with ocular MG develop into generalized MG
low‑frequency repetitive nerve stimulation (RNS) tests. during a 13‑year follow‑up period. These differences in
the rate of secondary generalization might be attributed
In 1997, Wang et al. [31] proposed a new clinical to the difference in race, severity of disease and early
absolute and relative score system for MG in Chinese treatment with immunosuppressive drugs, especially
patients.The absolute scoring system consists of 8 corticosteroids. [38,40]
items: ptosis, palpebra superior fatigability, disability
of ocular motion, fatigability of the upper and lower Given the poor prognosis of generalized MG, it is
extremity muscles, disability of facial muscles, chewing important to detect the risk factors of secondary
difficulties, dysphagia and disability of respiratory generalization in those MG patients with initial ocular
muscles, with a score of each item ranging from presentations. Previous studies have revealed that
0 (normal) to 4 (severe dysfunction). The relative scores onset age > 15 years, presence of thymoma, early
are obtained by subtracting the pretreatment scores corticosteroids therapy and abnormal RNS results
from the posttreatment scores and then dividing the on stimulating proximal limb muscles are predictors
results by the pretreatment scores. Several studies have for the development of generalized MG. [39,41‑43] Our
proven that the clinical absolute and relative scoring recent study has shown that disease onset during
system has good reliability and sensitivity to evaluate adulthood and RNS abnormality of the facial nerve
the disabilities in MG patients [31,32] and the clinical predict the progression from ocular to generalized
absolute and relative system is officially recommended MG while course of the disease is inversely correlated
by the Consensus of Chinese Experts in the Diagnosis with secondary generalization (unpublished data).
and Treatment for Myasthenia Gravis. [33] In a senior population, the ocular MG patients with
anti‑AChR antibodies, antistriated muscle antibodies,
SECONDARY GENERALIZATION abnormal RNS findings and abnormal single fiber
electromyography tend to develop generalized MG. [44]
Generalization of clinical symptoms is an important However, other studies have demonstrated that none
hallmark of MG patients. Ocular MG is termed when of these factors significantly predict development
weakness is only limited to the extra‑ocular muscles of generalized MG in younger populations. [2,45,46]
for > 2 years, [34,35] while generalized MG is defined Although similar results have been obtained in some
as an extension of weakness beyond ocular muscles. studies, there are also some limitations such as the
The involvement of muscles is confirmed mainly by use of retrospective methodology, incomplete clinical
clinical presentations. Due to the different involvement data, small sample size and single hospital or center.
of muscle groups, clinical presentation varies from Larger‑sample, multi‑center, prospective studies are
fluctuating extra‑ocular muscular weakness to needed to obtain more convincing risk factors for
respiratory failure. Secondary generalization mainly generalization of ocular MG.
occurs during the first 2 years [16,36] and sometimes leads
to the deterioration of prognosis including death. ACKNOWLEDGMENTS

It is well‑known that ocular muscle weakness is the This work was supported by the National Natural Science
most common initial symptoms of MG, occurring in Foundation of China (Nos. 31200665, 31270952 and
approximately 85% of patients. About 50% of these 81301069).
ocular MG patients may progress to generalized MG
within 6 months after onset, 80% of patients within REFERENCES
1‑year, and 90% of patients after 3 years. Only 10% of
MG patients do not progress to secondary generalization 1. Vincent A, Palace J, Hilton‑Jones D. Myasthenia gravis. Lancet
2001;357:2122‑8.
throughout lifetime. Another published study has 2. Bever CT Jr, Aquino AV, Penn AS, Lovelace RE, Rowland LP.
[2]
reported that up to 65% of MG patients initially show Prognosis of ocular myasthenia. Ann Neurol 1983;14:516‑9.

Neuroimmunol Neuroinflammation | Volume 1 | Issue 3 | December 2014 129