Evaluation of the slap test using ultrasonography

Introduction

Laryngeal hemiplegia (LH) or recurrent laryngeal neuropathy (RLN) is an idiopathic distal axonopathy that prevents maximum laryngeal dilatation, there is a failure in the abduction of the arytenoid cartilage due to the absence or motor decrease of the dorsal cricoarytenoid muscle, the narrowing of the rima glottidis decreases the air intake to the lungs and may limit athletic performance. The slap test (ST) induces the thoraco-laryngeal adductor reflex, this is currently widely used in the physical and endoscopic examination for the diagnosis of this condition. Ultrasound is a portable, fast, non-invasive, innocuous, and accessible method by means of which we can visualize the movement of the vocal cords.

Objective: Evaluation of the slap test under ultrasonographic visualization.

Materials and Methods

The evaluation of ST was performed in the physical, endoscopic and ultrasonographic examination of 20 equines. Prior to the ultrasound study a tricotomy of the ventral aspect of the laryngeal region was performed, was used Sonoscape E2 ultrasound with a linear transducer at a frequency of 7.5MHZ. The transducer was placed perpendicular to the mandibular branches. The thoraco- laryngeal adductor reflex was induced by performing a slap on the caudal angle of the scapula on both sides.

Results

In 16 equines the ST evaluation was positive, and movement of both arytenoid and vocal cords could be detected by physical, endoscopic and ultrasound examination. In 4 of the equines the ST evaluation by physical, endoscopic and ultrasound examination was negative on the left side and positive on the right side.

Conclusion

Currently endoscopy is the most widely used complementary method to evaluate laryngeal functionality in the equine, however, ultrasonography represents a faster, safer and non-invasive diagnostic method that allows visualization of the vocal folds movement at the time of performing the ST, being a very useful, objective, accessible and uncomplicated tool for the diagnosis of LH.

References

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