Mitochondrial abnormalities of late motor neuron degeneration following poliomyelitis and other neurogenic muscular atrophies

Human motor endplate remodeling after traumatic nerve injury

OBJECTIVE

Current management of traumatic peripheral nerve injuries is variable with operative decisions based on assumptions that irreversible degeneration of the human motor endplate (MEP) follows prolonged denervation and precludes reinnervation. However, the mechanism and time course of MEP changes after human peripheral nerve injury have not been investigated. Consequently, there are no objective measures by which to determine the probability of spontaneous recovery and the optimal timing of surgical intervention. To improve guidance for such decisions, the aim of this study was to characterize morphological changes at the human MEP following traumatic nerve injury.

METHODS

A prospective cohort (here analyzed retrospectively) of 18 patients with traumatic brachial plexus and axillary nerve injuries underwent biopsy of denervated muscles from the upper extremity from 3 days to 6 years after injury. Muscle specimens were processed for H & E staining and immunohistochemistry, with visualization via confocal and two-photon excitation microscopy.

RESULTS

Immunohistochemical analysis demonstrated varying degrees of fragmentation and acetylcholine receptor dispersion in denervated muscles. Comparison of denervated muscles at different times postinjury revealed progressively increasing degeneration. Linear regression analysis of 3D reconstructions revealed significant linear decreases in MEP volume (R = -0.92, R2 = 0.85, p = 0.001) and surface area (R = -0.75, R2 = 0.56, p = 0.032) as deltoid muscle denervation time increased. Surprisingly, innervated and structurally intact MEPs persisted in denervated muscle specimens from multiple patients 6 or more months after nerve injury, including 2 patients who had presented > 3 years after nerve injury.

CONCLUSIONS

This study details novel and critically important data about the morphology and temporal sequence of events involved in human MEP degradation after traumatic nerve injuries. Surprisingly, human MEPs not only persisted, but also retained their structures beyond the assumed 6-month window for therapeutic surgical intervention based on previous clinical studies. Preoperative muscle biopsy in patients being considered for nerve transfer may be a useful prognostic tool to determine MEP viability in denervated muscle, with surviving MEPs also being targets for adjuvant therapy.

Focal deficiency of cytochrome-c-oxidase in skeletal muscle of patients with progressive external ophthalmoplegia. Cytochemical-fine-structural study

In skeletal muscle biopsies of 8 patients with progressive external ophthalmoplegia combined light and fine structural cytochemical studies of cytochrome-c-oxidase revealed the absence of the enzyme in single fibres with or without accumulation of abnormal mitochondria. However, some fibres showed abnormal mitochondria without any deficiency of the enzyme. In one case with only slight mitochondrial proliferation the existence of the enzyme defect was the most remarkable finding. The occurrence of the enzyme defect obviously does not depend on concomitant structural alterations of the chondriom. The results are consistent with an acquired mitochondrial injury leading to a gradual loss of enzyme activity either earlier (with or without a minimal reactive mitochondrial proliferation) or later (after a phase of mitochondrial proliferation) in the course of the disease. Focal lack of cytochrome-c-oxidase activity is apparently a constant feature of the syndrome; it therefore may be not only of pathogenetic but also of diagnostic importance and in this connection cytochemical-fine-structural demonstration of cytochrome-c-oxidase is a valuable method. In contrast to the biochemical approach it allows not only the detection but also the exact anatomical localization of single fibre defects.

Mixed nemaline-mitochondrial "myopathy"

A 4-year-old boy suffering from a nonprogressive muscular weakness had a muscle biopsy which ultrastructurally showed large aggregates of nemaline bodies and mitochondria in myofibers; occasional concentric lamellated bodies were present as well. The mitochondria were mostly at the periphery of collections of nemaline bodies, less commonly in their central portions. The light microscopic features differed from those of either nemaline or mitochondrial myopathy and were somewhat reminiscent of multicore disease. Evidence suggestive of possible neurogenic origin of both rods and mitochondria is reviewed.