Disuse atrophy of the muscle occurs i.e., shrinkage of muscle fibre finally replaced by fibrous tissue (fibrous muscle)
Other causes include Guillain–Barré syndrome, West Nile fever, C. botulism, polio, and cauda equina syndrome; another common cause of lower motor neuron degeneration is amyotrophic lateral sclerosis. Diagnosis
Differential diagnosis
Myasthenia gravis – synaptic transmission at motor end-plate is impaired
Amyotrophic lateral sclerosis – causes death of motor neurons, although exact cause is unknown it has been suggested that abnormal build-up of proteins proves toxic for the neurons. See also
Lower motor neuron
Upper motor neuron
Upper motor neuron lesion

References
External links

http://library.med.utah.edu/neurologicexam/html/motor_anatomy.html#06
Silent sinus syndrome is a spontaneous, asymptomatic collapse of an air sinus (usually the maxillary sinus and orbital floor) associated with negative sinus pressures. It can cause painless facial asymmetry, diplopia and enophthalmos. Diagnosis is suspected based on symptoms, and can be confirmed using a CT scan. Treatment is surgical involving making an outlet for mucous drainage from the obstructed sinus, and, in some cases, paired with reconstruction of the orbital floor. It is slightly more common in middle age. Signs and symptoms
Silent sinus syndrome can cause facial asymmetry (usually without pain), and vision problems (such as diplopia and enophthalmos). It may also cause headaches, and a feeling of fullness in the nose. Mechanism
Silent sinus syndrome most often affects the maxillary sinus, usually with a collapse of the orbital floor. It may also affect the frontal sinus or the ethmoid sinus. When the maxillary sinus is involved, the inferior oblique muscle may be damaged.The cause of silent sinus syndrome is not well understood. Bacteria in the maxillary sinus may be involved. The connection to the nose may be blocked. This can create negative pressure in the sinus, as secretions are reabsorbed. Diagnosis
Silent sinus syndrome is first suspected based on symptoms. A CT scan can be used to confirm a diagnosis. This can have characteristic features, including maxillary sinus outlet obstruction, sinus opacification, and sinus volume loss caused by inward retraction of the sinus walls. Differential diagnosis
Silent sinus syndrome is a subtype of stage three chronic maxillary atelectasis.