| ObjectivesThis study was aimed to investigate the clinical and electrophysiological characteristics of patients with polymyositis.Materials and methods1. The clinical data of 93 consecutive patients with PM admitted to Chinese PLA General Hospital between 2006 and 2010 were summarized.2. The parameters of EMG from 93 PM patients were analyzed. The positive rates of EMG myopathic pattern in different muscles were compared. The EMG patterns in patients with different disease course were also analyzed.3. The clinical and EMG features of patients with isolated PM were compared with those of patients with interstitial lung disease (ILD) and patients associated with a connective-tissue disorder.4. The characteristics of EMG and serum levels of CK, LDH, ALT and AST in patients with prior corticosteroids treatment were compared with those of patients without prior specific treatment.5 The clinical and electrophysiological features were decribed in patients with mixed electrophysiological changes.Results1. The mean age of 93 PM patients was 43.19±15.64 years.25.81% of patients were male and 74.19% of them were female. The male/female ratio was 1:2.9. The mean course of disease was 19.16±33.123 (0.3-228) months.18 patients (19.35%) had ILD.17 patients (18.28%) were associated with a connective-tissue disorder, in which,5 patients (29.41%) had rheumatoid arthritis. One patient (1.08%) had non-Hodgkin's lymphoma.36 PM patients (38.71%) were taking corticosteroids at the time of initial EMG examination. Serum CK, LDH, AST, ALT and ESR were elevated in 83.87%,97.33%,85.07%,88.06% and 65% patients respectively. Muscle biopsy was performed in 40 cases,32 (80%) of them showed pathological features consistent with myositis,7 of them (17.5%) showed non-specific muscle fiber necrosis but without inflammatory cell infiltration,1 (2.5%) case was normal histologically.2. Electrophysiological data (biceps brachii, abductor pollicis brevis, quadriceps femoris, tibialis anterior) of 93 PM patients:abnormal insertional potential was observed in 15.88%, fibrillations was observed in 68.80%, positive sharp waves was observed in 66.85%, CRDs was observed in 6.45% of the muscles tested. The short duration MUPs were observed in 79.94% of the muscles tested. Over 20% increment of polyphasic MUPs was observed in 14.48% of the muscles tested. The myopathic interference pattern (IP) was observed in 9.74% of the muscles tested. The short duration MUPs were the most sensitive electrophysiological parameter in PM patients. The mean amplitude of MUPs (biceps brachii, abductor pollicis brevis, quadriceps femons, tibialis anterior) were 400.39±76.12μV,452.1±88.4μV,447.39±77.1μV and 468.03±214.09μV respectively. The difference of abnormal EMG findings between biceps brachii and quadriceps femoris, quadriceps femoris and tiabialis anterior were not statitically significant (P>0.05). The abnormal EMG findings were more frequent in tibialis anterior than in abductor pollicis brevis (abnormal insertional potential, fibrillations and positive sharp waves, short duration MUPs, over 20% increment of polyphasic MUPs, myopathic IP) (P=0.04,0.001,0.000,0.045,0.018). The abnormal EMG findings were more frequent in biceps brachii than in abductor pollicis brevis (abnormal insertional potential, fibrillations and positive sharp waves, short duration MUPs, over 20% increment of polyphasic MUPs, myopathic IP) (P=0.003,0.008,0.000,0.002).3. The ALT level was higher and the mean amplitude of MUPs (biceps brachii) was lower in patients with a history longer than 3 months than those with a history shorter than 3 months (P<0.05).4. All PM cases were divided into two groups. Group A:without ILD,74 cases, mean course:21.77±4.21 months, mean age:49.16±15.10 years. Group B: with ILD,19 cases, mean course:9.02±2.85 months, mean age:41.67±15.51 years. The course was longer in patients in Group A than that of in Group B (P<0.05). The mean age was not statistically different between the two groups. The serum level of CK and LDH in Group A were significantly higher than those in group B. The abnormal EMG findings in biceps brachii and quadriceps femoris in Group A (abnormal spontaneous activity, short duration MUPs, myopathic IP) were significantly more frequent than those in group B (P=0.05,0.00,0.05). Short duration MUPs in tiabialis anterior in group A was more frequent than that in group B (P=0.02). The decrement of mean amplitude of MUPs in tiabialis anterior in group A (440.8±96.59μV) was greater than that in group B (573.79±426.13μV) (P=0.012).5. The abnormal EMG findings, serum level of CK, LDH, ALT and AST, ESR were not statistically different between isolated PM patients and PM patients associated with connective tissue disease, PM patients without corticosteroids treatment 3 months prior to EMG examination and those with corticosteroids treatment.6. The isolated myopathic EMG pattern was detected in 86 of 93 PM patients (92.47%). Three cases were myopathic pattern combined with neurogenic pattern (3.23%), one patient had diabetes mellitus. Nerve conduction study revealed MCV and SCV decrement with reduction of CMAP and SNAP amplitude in nerves in two cases. SCV decrement was detected in median nerve in one case. Thus, myopathic EMG pattern was detected in 89 of 93 PM patients (95.7%). The other 4 cases din't show definite myopathic EMG pattern, but slight decrement of mean duration of MUPs was seen in some muscles in two cases and abnormal spontaneous potensials were detected in tibialis anterior in one case. Among the four cases, one was pathologically proved to be inflammatory myopathy, and the other three cases had prior corticosteroids treatment with clinical improvement before EMG examination.Conclusions1. EMG was essential for the diagnosis of PM. Short duration MUPs was the most sensitive and significant parameter. The difference of myopathic EMG pattern between proximal and distal muscles was detected in the upper extremities, but not in the lower extremities.2. The mean amplitude of MUPs in biceps brachii might be lower in patients with longer course. The course of PM patients without ILD was longer than that of PM patients with ILD. And, the abnormal EMG findingds and elevated serum levels of CK and LDH indicated that muscle damage might be severe in PM patients without ILD.3. The neurogenic EMG pattern in PM may be caused by complicated neuropathy. 4. Isolated neurogenic EMG pattern was not found in this series of PM cases.Keywordspolymyositis; electromyogram; retrospective analysis; interstitial lung disease; creatine kinase... |
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