What causes stapedius paralysis and symptoms?

Stapedius paralysis occurs when the nerve to the stapedius (a branch of the facial nerve or cranial nerve VII) is damaged, preventing the muscle from contracting properly. This leads to loss of the stapedial reflex and results in heightened sound sensitivity known as hyperacusis—a condition in which normal sounds are perceived as abnormally loud or painful.

Causes of Stapedius Paralysis

1. Facial Nerve Damage
   • Damage to the facial nerve before the branch to the stapedius muscle diverges leads to paralysis of the stapedius.
   • Common in Bell’s Palsy, an idiopathic facial nerve paralysis affecting one side of the face.
2. Infectious Causes
   • Viral infections such as Herpes Zoster (Ramsay Hunt Syndrome) cause inflammation of the facial nerve, leading to stapedius dysfunction.
   • Bacterial infections like otitis media or cholesteatoma may also damage the facial canal, affecting the nerve supply.
3. Trauma or Surgery
   • Fractures of the temporal bone or ear surgeries (especially stapes or mastoid operations) can injure the facial nerve or the stapedius tendon directly.
4. Congenital Absence or Anomalies
   • Rarely, there can be congenital absence of the stapedius muscle or its tendon, seen in about 0.5% of individuals, often associated with other middle ear defects.
5. Post-Paralysis Synkinesis
   • During recovery from facial paralysis, abnormal nerve regrowth can cause stapedial synkinesis, where facial movements trigger unwanted stapedius contractions, leading to distorted hearing.

Symptoms of Stapedius Paralysis

• Hyperacusis: Normal sounds (e.g., voices, clapping, or music) seem uncomfortably loud due to lack of stapes damping.
• Distorted Hearing: Some patients experience muffled or rumbling sounds during facial movements because of nerve misconnection during recovery (synkinesis).
• Sound-Induced Discomfort or Pain: Sudden noises may cause vibration-induced pain in the affected ear.
• Associated Facial Weakness: Since stapedius paralysis often accompanies facial nerve lesions, symptoms like facial droop, loss of expression, or drooling may also appear.