Was diagnosed with PLS with myopathy in2012. I have some muscle wasting with increased muscle tone. Why do I have increased tone with muscle wasting?

PLS. Primary lateral sclerosis (PLS) is a rare neuromuscular disease with slowly progressive weakness in voluntary muscle movement. PLS belongs to a group of disorders known as motor neuron diseases. PLS affects the upper motor neurons in the arms, legs, and face. Symptoms include weakness, muscle stiffness and spasticity, clumsiness, slowing of movement, and problems with balance and speech.