There are a number of autoimmune and deposition diseases that are thought to cause facial weakness. Amyloidosis is a condition where the protein amyloid builds up in certain kinds of cells, and essentially prevents some cells and tissues from functioning normally. There are certain types of amyloidosis that cause bilateral progressive facial paralysis, and result in loss of expressions unless facial reanimation is pursued. Sarcoidosis is another disease where the body forms granulomas in different cells and tissues, and has a similar effect on facial function. Both Guillain-Barré syndrome and its facial variant, Miller-Fisher syndrome, can cause abrupt onset facial weakness (over the course of hours to a few days) on one or both sides of the face, followed by recovery. However, in these conditions, recovery can sometimes be disorganized, and patients can experience over-recovery that requires treatment with physical therapy, chemodenervation with Botox, and other maneuvers to improve overall appearance.
Multiple sclerosis is a demyelinating disease, which sometimes leads to facial weakness. It tends to wax and wane as does the disease itself, so patients can experience prolonged facial weakness in one segment or one side of the face, and then essentially completely recover to normal.
A syndrome has been described that involves multiple episodes of facial weakness on either side of the face, accompanied by episodes of facial swelling. These patients, who often also have a fissuring, or prominent line in the center of their tongue, are deemed to have Melkersson Rosenthal syndrome. This condition is diagnosed by recognizing the triad of facial palsy, lip or face swelling, and a fissured tongue. It can also be confirmed by finding granulomas in a biopsy of the lip, usually during one of these episodes of facial or lip swelling. Patients with this condition have been shown to have fewer episodes of future facial weakness if they undergo facial nerve decompression surgery, where some of the bone around the facial nerve in the skull is removed to give the facial nerve more room for episodic swelling.