Trochlear nerve palsy is a clinical syndrome that occurs when the trochlear nerve is stimulated, compressed, or damaged by various causes, affecting the area it innervates.
The trochlear nucleus is located in the anterior part of the central gray matter of the midbrain and primarily innervates the superior oblique muscle.
Key Diagnostic Points
There are two main causes.
1. Intracranial Lesions
Conditions such as brainstem tumors, otitis media (complicated by basilar meningitis), thrombotic cerebral venous sinusitis, syphilis, and tuberculous encephalitis can either directly compress the trochlear nucleus or cause paralysis by stretching the trochlear nerve secondary to increased intracranial pressure.
II. Extracranial Lesions
Such as viral infection, periorbital cellulitis, periostitis, trauma, etc., directly or indirectly compress or affect the trochlear nerve.
In patients with clinical trochlear nerve palsy, the affected eye is slightly lower than the healthy side. Except when looking upward and outward (no diplopia occurs), diplopia is present in all other directions of gaze. A common chief complaint is difficulty descending stairs due to diplopia. When looking vertically upward, the average separation between the two eyes is 10–20 degrees, and during convergence movements it rarely exceeds 3 degrees. In some cases, the upper eyelid of the healthy side may be slightly lower than that of the affected side, which is often mistaken for partial oculomotor nerve palsy on the healthy side. This phenomenon is thought by some to be caused by excessive relaxation of the levator palpebrae superioris muscle on the healthy side.
Examination: When the presence or absence of trochlear nerve palsy is uncertain, the following observations can aid diagnosis:
When the patient looks upward or toward the unaffected side, the eye on the paralyzed side deviates markedly upward.
2. Head Tilt Test: When the head tilts to one side, under normal physiological conditions both eyes rotate toward the opposite side; in the case of superior oblique muscle paralysis, they rotate downward. Patients often tilt their head toward the healthy side to avoid diplopia. In superior oblique muscle paralysis, the diplopia test reveals a virtual image. For example, in right superior oblique muscle paralysis, the virtual image is located to the right and below the real image. When both eyes look downward and to the right, the vertical distance between the real and virtual images is greatest.
Treatment
I. Acupoints and Needling Methods
1. **GB14 (Yangbai)** (affected side): Located on the forehead, 1 cun directly above the midpoint of the eyebrow. A gauge-30, 1.5 cun filiform needle is used. After routine local disinfection, insert obliquely toward **EX-HN4 (Yuyao)** to a depth of approximately 1.2 cun. Needling sensation: Distending pain in the forehead and orbital region.
2. **Taiyang (EX-HN5) (affected side):** Located in the depression about 1 *cun* posterior to the midpoint between the lateral end of the eyebrow and the outer canthus. Use a gauge 30, 1.5 *cun* filiform needle. After routine local disinfection, insert horizontally toward **ST8 (Touwei)** to a depth of approximately 1.4 *cun* (reaching the temporal bone). Needling sensation: distension and pain in the temporal region, or radiating distension and pain to the inner-upper aspect of the eyeball.
3. GB37 (Guangming) (healthy side): 5 cun above the lateral malleolus, on the anterior border of the fibula, between the extensor digitorum longus and…
Between the peroneus brevis muscles; use a 30-gauge, 2-cun filiform needle. Perform routine local disinfection, then insert perpendicularly to a depth of approximately 1.8 cun. Needle sensation: radiates toward the dorsum of the foot or the heel.
2. Methods
The affected side is selected. The patient takes a sitting position. After the above points are inserted according to the standard method, electrical stimulation is applied to GB14 (Yangbai) and EX-HN5 (Taiyang). The needles are retained for 40 minutes. Treatment is given once daily, with 6 sessions constituting one course. A 5-day rest is taken before the next course.
[Commentary]
Trochlear nerve palsy presents with relatively mild clinical manifestations, making diagnosis challenging. For simple trochlear nerve palsy, the above treatment method (acupuncture) yields excellent results. If the condition is caused by intracranial inflammation, tumors, or other factors, the underlying cause should first be addressed before initiating acupuncture, which can also achieve satisfactory outcomes. During the treatment period, patients should wear glasses with the affected side’s lens covered by gauze to avoid discomfort in the affected eye and interference with treatment.