Pyridostigmine (PD), a muscarinic cholinergic agonist, and arginine (ARG) clearly increase the growth hormone (GH) response to growth hormone-releasing hormone (GHRH) in man. The current study was undertaken to investigate the value and safety of PD + GHRH and ARG + GHRH tests as well as the measurement of serum insulin-like growth factor I (IGF-I) in diagnosing GH deficiency in adults. Fifty-four patients considered GH deficient from extensive organic or idiopathic pituitary disease and 326 healthy adults were studied. The IGF-I concentrations were lower than the 3rd percentile of normal values in only 31 of the 54 (57.4%) patients with hypopituitarism. However, the IGF-I levels in hypopituitary patients and in normal subjects overlapped more frequently between 41 and 60 years (50%) and between 61 and 80 years (92.3%) as opposed to between 20 and 40 years (8.6%). In contrast to the IGF-I measurement, the ranges of peak GH responses to PD + GHRH and ARG + GHRH tests were clearly differentiated between the hypopituitary (0.2-6.8 and 0.1-9.5 microg/l, respectively) and normal (17.7-114 and 16.1-119 microg/l, respectively). However, the PD + GHRH test was reliable only in subjects of 20-40 years of age. In conclusion, IGF-I measurement had no value in the diagnosis of GH deficiency in adults aged over 40 years, but is reliable enough when young adults of 20-40 years of age are considered. Both PD + GHRH and ARG + GHRH testing should be considered more reliable biochemical measurements of GH deficiency. In contrast to the PD + GHRH test, the ARG + GHRH test is reliable throughout the adult lifespan and appears to be the most appropriate for patient compliance and safety.
The GHRH test has been proposed to replace conventional stimuli in the diagnosis of GH deficiency. However the reliability of GHRH in discriminating between normal and GH-deficient children is still uncertain. The aim of this study was to compare the GH-releasing effect of GHRH (1 microgram/kg i.v.) with that of two neuroactive drugs, clonidine (CLON, 150 micrograms/m2 orally), an alpha 2-receptor agonist, and pyridostigmine (PD, 60 mg orally), a cholinergic agonist that inhibits cholinesterases, in 23 children and adolescents with normal and familial short stature. The plasma GH peak (mean +/- SEM) after GHRH (20.3 +/- 2.5 ng/ml), CLON (17.0 +/- 2.1 ng/ml) and PD (14.9 +/- 1.5 ng/ml) did not significantly differ. According to the conventional limit (less than 10 ng/ml), a false negative response was present in 6, 5 and 6 subjects after GHRH, CLON and PD, respectively. In conclusion, GHRH, CLON and PD have a similar GH-releasing effect. A similar percentage of false negative responses was observed with all tests and this evidence reduces their diagnostic ability.
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Given the safety and efficacy of this medication, pyridostigmine should be considered to modulate severe sequelae of botulinum toxin in select patients when conservative management is deemed insufficient. Also, physicians should be aware that patient complaints of symptoms at distant sites and temporally delayed from the injection may be a result of the botulinum toxin and relieved with pyridostigmine.
GFPT1-myasthenia is more heterogeneous than previously reported. Different parameters of neuromuscular transmission are variably affected. When disruption of muscle-specific isoform determines the phenotype, this has devastating clinical, pathologic, and biochemical consequences.
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A successful pregnancy with a healthy infant was achieved after fetal exposure to 3,4-DAP and pyridostigmine.
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The inhibition of human and mammalian red blood cell (RBC) cholinesterase (AChE) in whole blood in the presence of added pyridostigmine has been examined. After the addition of pyridostigmine to animal and human blood, red cells were separated from plasma at varying intervals and their enzyme activity measured. An apparent rate constant (ke) was derived for the reaction sequence in which carbamate is released from AChE inhibited by pyridostigmine. The constant is a complex of the rates of decarbamoylation and reinhibition of AChE in the blood sample. Rate constants were also determined for the spontaneous reactivation (ks) of carbamoylated AChE in the species studied. Values of Ks were greater than Ke in corresponding species but varied little between species. Pretreatment of animals with pyridostigmine is known to be an effective therapy against organophosphorus compounds, including soman. The ranking of ke values in mammalian blood was the same as that for the protection against soman in animals: monkey greater than guinea-pig greater than rabbit greater than rat (ke = 0.15, 0.07, 0.05, 0.02 h-1, respectively). Since ke for human blood (0.20 h-1) was greater than that of monkey, pyridostigmine pretreatment would be expected to be an effective prophylaxis for soman in humans.
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Study results provide preliminary evidence that military personnel with certain BChE genotypes who used PB during the 1991 Gulf War may have been at particularly high risk for developing GWI. Genetic differences in response to wartime exposures are potentially important factors in GWI etiology and should be further evaluated in conjunction with exposure effects.
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The data reviewed in this paper indicate that spontaneous fibrillations do not involve a cholinergic mechanism since non-depolarizing anticholinesterase drugs such as Mestinon fail to increase spontaneous fibrillations in denervated muscle. Fibrillation potentials are related to the changes in electrical properties of the membrane of denervated muscle fibres which lead to the appearance of spontaneous subthreshold depolarizations, sometimes triggering a propagated potential. Fibrillations seem to appear in cycles and this may depend on the depression of spontaneous depolarization by muscle activity itself. Fibrillations are also an important feature of Duchenne muscular dystrophy and polymyositis, but they have not been found in Landouzy-Dejerine muscular dystrophy. These "myopathic" fibrillations probably arise from subthreshold depolarizations in the membrane of muscle fibre segments which have been functionally or anatomically isolated from the end-plate by a pathological lesion (Fig. 4). Experimental demonstration of spontaneous fibrillations in baboon biceps muscles after extrajunctional myotomies indicates that such an isolated muscle fibre segment can indeed develop and sustain spontaneous fibrillation activities. Studies of motor unit potentials in myopathies by "coherent" electromyography disclose linked potentials after the main potential in Duchenne dystrophy, but not in Landouzy-Dejerine muscular dystrophy. The linked potentials are signs of collateral innervation by sprouts of the motor axons. The fact that linked potentials occur in Duchenne dystrophy, including in obviously dystrophic motor units (Fig. 5), shows that such motor axons are quite healthy and able to sprout efficiently. The muscle fibres thus innervated collaterally are probably the ones which fibrillated and were deprived of trophic motor control as a result of myopathic lesions of the type considered in Fig.4. This correlation receives support from the finding that both spontaneous fibrillations and linked potentials are lacking in Landouzy-Dejerine muscular dystrophy, which obviously presents a different type of muscle lesion.
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A 91-year-old man was diagnosed with ocular myasthenia gravis. He was started on pyridostigmine, and 2 weeks later he developed a rash. The rash was biopsied and found to be secondary to leukocytoclastic vasculitis; the pyridostigmine was stopped, loratadine was started, and the rash resolved.
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In 54 patients (69%) symptoms and signs remained confined to the extraocular muscles during the observation period. The remaining 24 patients (31%) developed symptoms of generalised myasthenia gravis; 50% of them within two years, 75% within four years after onset. A somewhat reduced risk of generalisation was found in those with mild symptoms, normal repetitive nerve stimulation test, and low or absent antiacetylcholine receptor (AChR) antibodies at the time of diagnosis. Patients receiving immunosuppressive treatment (corticosteroids and/or azathioprine) rarely developed generalised myasthenia gravis (six of 50, 12%). Those without such treatment, usually due to uncertain diagnosis and late referral, converted into generalised myasthenia gravis significantly more often (18 of 28, 64%).