Enlargement of the Nissl substance as a manifestation of early damage to spinal cord motoneurons in amyotrophic lateral sclerosis

Aims: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of motoneurons. Recent studies indicate that in ALS, degeneration of motoneuron body is late in comparison to degeneration of axons. The morphological consequence of the axonal damage is chromatolysis. Therefore, loss of tigroid in motoneurons as a morphological manifestation of chromatolysis should be a prominent feature seen in an early stage of the disease. To verify that assumption we examined morphologically spinal cord motoneurons in patients with sporadic ALS. Material and methods: In anterior horn motoneurons of 33 patients tigroid were assessed at light microscopy and morphometrically analyzed. Material was divided into an acute ALS group with a duration of the disease of up to 1 year, and a chronic ALS group with a clinical course lasting for 4 - 9 years. Results: In the acute ALS group, loss of motoneurons was slight, and only a part of them showed central chromatolysis. Instead of chromatolysis the enlargement of the tigroid was found. This phenomenon was observed only in acute ALS and confirmed by morphometric analysis. Conclusions: In ALS, enlargement of the tigroid seems to be an early morphological feature occuring earlier than central chromatolysis. Its presence may be connected with endoplasmic reticulum stress, disturbed axonal transport or functional compensation of the neuronal deficit.