Which of the following nerves is responsible for referred otalgia from tonsillitis?

Correct Answer: A. Glossopharyngeal nerve

The glossopharyngeal nerve (CN IX) is the sensory innervation of the oropharynx and palatine tonsils. When the tonsils are inflamed (tonsillitis), the inflammatory stimulus activates sensory fibres of CN IX. These visceral afferent fibres travel centrally and converge with somatic sensory fibres of the vagus nerve (CN X) and trigeminal nerve (CN V) in the trigeminal nucleus in the medulla. This convergence at the spinal trigeminal nucleus is the anatomical basis of referred pain — the brain misinterprets the visceral pain signal as originating from the somatic distribution of CN V (ear and temporal region). This is why patients with acute tonsillitis classically present with otalgia (ear pain) despite the pathology being in the pharynx. The CN IX pathway is the primary sensory supply to the tonsils, making it the discriminating answer. In Indian clinical practice, otalgia is a cardinal presenting symptom of tonsillitis in children and adults, and recognizing this referred pain pattern is essential for correct diagnosis and avoiding unnecessary otological investigations.

Why the other options are wrong

B. Trigeminal nerve — The trigeminal nerve (CN V) innervates the external ear, temporal region, and anterior two-thirds of the tongue, but NOT the tonsils or oropharynx. While CN V is the somatic nerve that receives the referred pain signal in the trigeminal nucleus, it is not the primary sensory nerve of the tonsils. This is the NBE trap — confusing the nerve that carries referred pain with the nerve that originates the pain signal. C. Vagus nerve — The vagus nerve (CN X) does innervate parts of the pharynx and larynx, but the palatine tonsils are specifically innervated by CN IX, not CN X. While CN X contributes to pharyngeal sensation, it is not the primary sensory supply to the tonsils. Students may confuse CN X's broad pharyngeal distribution with tonsillar innervation, but CN IX is the discriminating answer for tonsil-specific pathology. D. Facial nerve — The facial nerve (CN VII) provides taste to the anterior two-thirds of the tongue via the chorda tympani and innervates muscles of facial expression, but has no sensory role in the oropharynx or tonsils. This is a clear anatomical mismatch and represents a distractor for students unfamiliar with cranial nerve distributions in the pharynx.

High-Yield Facts

Mnemonics

CN IX = Tonsil Nerve (Glosso-Pharyngeal) Glosso = tongue base + Pharyngeal = pharynx/tonsils. CN IX carries taste and sensation from posterior third of tongue AND sensory innervation of tonsils. When tonsils hurt → CN IX fires → referred pain to ear via trigeminal convergence. REFERRED PAIN RULE: Origin ≠ Perception Tonsil pain originates from CN IX (visceral), but is perceived in CN V territory (ear/temporal). The brain mislocates it because both converge in the medulla. Tonsillitis = otalgia, not glossalgia.

NBE Trap

NBE pairs "otalgia" with "trigeminal nerve" to trap students who confuse the nerve carrying the referred pain signal (CN V) with the nerve that originates the pain (CN IX). The key discriminator is remembering that CN IX is the primary sensory nerve of the tonsils, not CN V.

Clinical Pearl

In Indian paediatric practice, a child presenting with otalgia and fever is often initially suspected of otitis media. However, otoscopy is normal, and the diagnosis becomes clear only when the pharynx is examined and inflamed tonsils are found. This is why CN IX's role in tonsillar innervation and referred otalgia is a high-yield clinical pearl — it prevents unnecessary antibiotic escalation and imaging in primary care settings.

_Reference: Bailey & Love Ch. 33 (Pharynx); Harrison Ch. 29 (Cranial Nerves); Robbins Ch. 16 (Head & Neck Pathology)_