Ricardo Maselli

Late Denervation in Patients with Antecedent Paralytic Poliomyelitis

The development of new weakness, fatigue, and pain decades after acute paralytic poliomyelitis is a recognized syndrome. We conducted a controlled study of this syndrome by analyzing clinical, electromyographic, and muscle-biopsy features in 18 patients with a history of poliomyelitis--13 reporting 1 to 20 years of new weakness and 5 without new symptoms. The patients with new weakness also reported new muscle atrophy (9 of 13) and fatigue (10 of 13), symptoms not reported by the controls. The age at the time of acute poliomyelitis, severity of poliomyelitis, residual disability, number of years since acute poliomyelitis, and age at the time of study were comparable in the weakening and control groups. Evidence of remote denervation consistent with antecedent poliomyelitis was demonstrated in all patients by electromyography or muscle biopsy or both. In addition, active denervation (as evidenced by spontaneous activity on conventional electromyography, increased jitter on single-fiber electromyography, or atrophic myofibers) was found in 12 patients in the weakening group and in all 5 controls. Immunohistochemical detection of myofibers expressing the neural-cell adhesion molecule corroborated ongoing denervation in both patient groups. When muscle data from both groups were pooled, correlations were observed between the extent of past reinnervation and the degree of ongoing motor-unit instability. We conclude that the extensive reinnervation of denervated muscle that occurs in paralytic poliomyelitis may be followed by late denervation of the previously reinnervated muscle fibers. Electromyographic and muscle-biopsy evidence of ongoing denervation does not distinguish between stable patients with prior paralytic poliomyelitis and those with new weakness.

Mutations in LAMB2 causing a severe form of synaptic congenital myasthenic syndrome

Background: We describe a severe form of congenital myasthenic syndrome (CMS) associated with congenital nephrosis and ocular malformations caused by two truncating mutations in the gene encoding the laminin β2 subunit (LAMB2). Methods and results: Mutational analysis in the affected patient, who has a history of a serious untoward reaction to treatment with acetylcholinesterase inhibition, revealed two frame-shifting heteroallelic mutations, a maternally inherited 1478delG and a paternally inherited 4804delC. An anconeus muscle biopsy demonstrated a profound distortion of the architecture and function of the neuromuscular junction, which was strikingly similar to that seen in mice lacking laminin β2 subunit. The findings included: pronounced reduction of the axon terminal size with encasement of the nerve endings by Schwann cells, severe widening of the primary synaptic cleft and invasion of the synaptic space by the processes of Schwann cells, and moderate simplification of postsynaptic folds and intact expression of the endplate acetylcholinesterase. The endplate potential quantal content was notably reduced, while the frequencies and amplitudes of miniature endplate potentials were only moderately diminished and the decay phases of miniature endplate potentials were normal. Western blot analysis of muscle and kidney tissue and immunohistochemistry of kidney tissue showed no laminin β2 expression. Conclusion: This case, which represents a new type of synaptic CMS, exemplifies the wide variability of phenotypes associated with LAMB2 mutations and underscores the fundamental role that laminin β2 plays in the development of the human neuromuscular junction.

Inflammation at the neuromuscular junction in myasthenia gravis

To better define the pathogenic mechanisms in the antibody-mediated autoimmune disease myasthenia gravis (MG), we analyzed the morphology and electrophysiology of the neuromuscular junction in anconeus muscle biopsy specimens from eight patients with MG and seven control subjects. There were inflammatory cells at the neuromuscular junction in seven of the eight biopsies from MG patients. The endplate index (length of the postsynaptic membrane divided by the length of the apposed presynaptic membrane) was abnormally reduced in all the MG patients, and fiber type grouping, suggestive of reinnervation, was present in six of the eight MG patients. Intracellular recording revealed diminished amplitude of miniature endplate potentials and miniature endplate currents in the MG patients compared with the controls. The time constant of decay of miniature endplate currents did not differ from that of controls, suggesting no change in mean channel open time of the acetylcholine receptor. The endplate receptor sensitivity to iontophoretically applied acetylcholine was also decreased in MG patients compared with controls. The quantal content of neurally evoked endplate potentials was reduced in six of the eight MG patients, demonstrating abnormal presynaptic function as well. The presence of inflammatory cells at the neuromuscular junctions of limb muscles in MG reconciles an apparent disparity between the animal model of MG, experimental autoimmune myasthenia gravis, and the human disease. This study also demonstrates a frequent presynaptic component to the abnormal neuromuscular transmission in MG.

Clinical studies with an aldose reductase inhibitor in the autonomic and somatic neuropathies of diabetes

Clinical investigations with the aldose reductase inhibitor (ARI) sorbinil in diabetic patients with neuropathy are described. Cardiac autonomic neuropathy was studied in 36 patients, in a double-blind, placebo-controlled, randomized, noncrossover trial. Patients received sorbinil (250 mg qd) or placebo over 6 weeks after a one-week baseline period. Diabetic control did not change over the study period, as indicated by unchanged glycohemoglobin. Response was assessed by expiration/inspiration (E/I) ratios on EKG during 6 c/min respiration and resting minimum heart rate, both measures of vagal function. In the sorbinil group, E/I ratios improved from 1.074 +/- 0.012 to 1.096 +/- 0.020 (P less than 0.03) with a slight decrease in the placebo group from 1.112 +/- 0.023 to 1.105 +/- 0.023 (P = NS). The difference between the week 6 and week 0 changes in each group was significant (P less than 0.01). Resting minimum heart rate decreased in the sorbinil group from 76.4 +/- 2.3 to 66.8 +/- 2.4 beats/min (P less than 0.001), with a mean change of 10 +/- 2. In the placebo group, heart rate was unchanged (77.9 +/- 3.9 to 77.5 +/- 3.3). The two sample t tests of the within-group differences were likewise significant (P less than 0.001). These changes in both E/I ratio and resting minimum heart rate are consistent with a sorbinil-related improvement in cardiac parasympathetic nerve function. Several isolated cases with apparent sorbinil-related improvement in autonomic symptoms will also be described. Studies of somatic neuropathy have previously shown improvement in nerve conduction velocities with sorbinil. In a study of 11 patients with severely painful diabetic neuropathy treated with sorbinil for 3 weeks [placebo-controlled in single-blind fashion (n = 8)], pains (as assessed on a 0 to 20 rating scale) improved from a mean score of 16 down to 8, with deterioration following drug withdrawal. Objective improvements in sensation and strength were observed in some cases. In this group of patients, statistically significant improvements in nerve conduction velocity, E/I ratios, and resting minimal heart rate, similar to those previously discussed, were also documented. Somatosensory-evoked potentials studies in the 36-patient study showed significant improvements in peripheral conduction and cortical responses. Sorbinil toxicity in 106 patients was 11.3%, with sex incidence of 7/73 males (9.6%) and 5/33 females (15.2%).(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Lymphocyte β‐Adrenergic Receptors in Multiple Sclerosis

We hypothesize that immune abnormalities in multiple sclerosis (MS), such as the reduction in suppressor cell function observed when disease is active, are linked to central nervous system (CNS) lesions that arise during the disease. The immune system is innervated by the sympathetic nervous system (SNS). Could strategically situated lesions, acting via the SNS, impair suppressor cell function and thereby favor progression? Many patients with MS have an exacerbating-remitting course at the outset and a progressive one later. We postulate that SNS-mediated signals may be involved. Abrogation of this SNS innervation in mice by chemical axotomy with 6hydroxydopamine alters immune function and causes splenic T and B cells to increase their P-adrenergic receptors severalfold, that is, they develop denervation hypersensitivity. 0-adrenergic receptor density in healthy humans is threefold greater on suppressor T cells (CDS +, 9.3 -) than on cytotoxic T cells (CD8 +, 9.3 ’). It seems reasonable to postulate that SNS influence on suppressor cells would predominate over its influence on other T-cell types. Could CNS damage in MS decrease SNS “tone” and in this way compromise suppressor function, thus setting the stage for a progressive course? Sympathetic nervous system ablation augments antibody production and up-regulates P-adrenergic receptor density on lymphocytes. Moreover, SNS ablation increases the severity of experimental allergic encephalomyelitis (EAE). (See paper by Schorr et al. in these proceedings.) We therefore thought it of interest to determine 0-adrenergic receptor density on lymphocytes from patients with progressive MS.

Effects of a monoclonal anti-acetylcholine receptor antibody on the avian end-plate.

1. The effects of anti‐acetylcholine receptor (AChR) monoclonal antibodies (mAbs) 370 and 132A on miniature end‐plate potentials (MEPPs) and end‐plate currents (EPCs) in the posterior latissimus dorsi muscle of adult chickens were investigated. 2. After incubation of the electrophysiological preparation with mAb 370 (5‐50 micrograms/ml), which blocks both agonist (carbamylcholine) and alpha‐bungarotoxin (alpha‐BTX) binding and induces a hyperacute form of experimental autoimmune myasthenia gravis (EAMG), MEPP and EPC amplitudes were irreversibly reduced. 3. This effect was not associated with any significant change in the time constant describing EPC decay (tau EPC), current reversal potential, or the voltage dependence of tau EPC. The tau EPC at ‐80 mV was 5.9 +/‐ 0.6 ms before incubation with mAb 370 (50 micrograms/ml) and 6.0 +/‐ 0.9 ms afterwards. Current reversal potential was ‐3.9 +/‐ 0.4 mV before mAb incubation and ‐4.8 +/‐ 1.5 mV afterwards. The change in membrane potential required to produce an e‐fold change in tau EPC was 128 +/‐ 2.3 mV before antibody incubation compared to 125 +/‐ 6.6 mV after incubation. 4. A second anti‐AChR mAb, 132A (50 micrograms/ml), which is capable of inducing the classically described form of EAMG without blocking agonist or alpha‐BTX binding, or inducing hyperacute EAMG, produced no significant change in MEPP amplitude, EPC amplitude, tau EPC or EPC reversal potentials. 5. The mAb 370 (50 micrograms/ml) induced a partially reversible decrease of the quantal content of the neurally evoked end‐plate potential (EPP). This effect was not observed with mAb 132A, (+)tubocurarine (10(‐7)‐10(‐5) g/ml) or an irrelevant anti‐oestrogen receptor mAb. 6. These data suggest that the rapid onset of weakness observed in chicken hatchlings after the injection of mAb 370 (Gomez & Richman, 1983) can be attributed to a combined effect of a block of acetylcholine (ACh)‐induced ion channel activity in the postsynaptic membrane and a reduction of the neurally evoked release of acetylcholine from the nerve terminal.

Experimental allergic neuritis in the SJL/J mouse: dysfunction of peripheral nerve without clinical signs

Experimental allergic neuritis (EAN) was studied in the SJL/J mouse and compared to EAN in the Lewis rat. The Lewis rat developed hind limb weakness and weight loss while the SJL/J mouse had no discernible clinical abnormalities. The SJL/J mouse, however, suffered subclinical damage to peripheral nerve (PN) myelin. Both species reproducibly developed electrophysiologic dysfunction of PN and histopathology confined to the peripheral nervous system (PNS). Understanding of autoimmune demyelination in the central nervous system was greatly enhanced by the development of experimental allergic encephalomyelitis in the SJL/J mouse. We believe that EAN in the SJL/J mouse could lead to a similar increase in our understanding of autoimmune demyelination in the PNS.