There are many neuromuscular disorders that produce generalized hypotonia. The approach to determining the etiology of neuromuscular hypotonia consists of establishing the site of dysfunction in the neuromuscular system (anatomical diagnosis), determining the most likely pathological process that affects the neuromuscular system at that particular location (pathological diagnosis), and finally determining the most likely etiology (etiological diagnosis), taking into account the suspected anatomical and pathological diagnoses.
The possible sites of dysfunction in the neuromuscular system can be schematically represented with a simplified model of the upper motor neuron system and the motor-sensory unit.

The upper motor neuron system is housed in the central nervous system. The relevant regions of the central nervous system in the understanding of generalized hypotonia are the brain, brainstem, cerebellum, rostral spinal cord, and brachial plexus (C5-T1) of the spinal cord (Figure 95.1)

Figure 95.1.— Schematic representation of the relevant regions of the central nervous system in the understanding of generalized hypotonia. C5-T1: brachial plexus region of the spinal cord.