Clinical Reasoning: Partial Horner syndrome and upper right limb symptoms following chiropractic manipulation

DISCUSSION

Our patient's ocular symptoms were consistent with Horner syndrome without anhidrosis, also referred to as partial Horner syndrome.³ Horner syndrome due to a herniated thoracic disc is considered very rare, and has to our knowledge only been reported 6 times in the English language literature,⁴ though never preceded by chiropractic manipulation.

Symptomatic thoracic disc herniation is uncommon and has been estimated to less than 0.75% of all symptomatic spinal disc herniations.⁵ Furthermore, more than 75% of thoracic protrusions are located below T8, and only approximately 3% occur at the T1-T2 level,⁵ as in our patient. Only 40 cases with a T1-T2 disc herniation have been reported since Svien and Karavitz presented their first case in 1959.^6,7

One of the most frequent causes of Horner syndrome is carotid artery dissection, which may occur spontaneously or due to local trauma to the neck region. Chiropractic manipulation as an independent risk factor for neck artery dissection and a consequent stroke is a controversial topic, though multiple cases of Horner syndrome due to ICA dissections subsequent to chiropractic manipulation have been reported.⁸ In our patient, an ICA dissection was considered unlikely due to the concomitant prominent radiating medial brachialgia and was furthermore ruled out by a CT angiogram of the neck vessels.

Lack of anhidrosis is indicative of either a postganglionic lesion at the ICA level, since sudomotor fibers are separated from the carotid plexus at the level of the carotid bifurcation, or alternatively a preganglionic sympathetic lesion of the T1 root, as the sudomotor fibers exit the spinal cord at the T2-T3 level (figure 3). Thus, rare cases of partial Horner syndrome due to lesions at the T1 root level should be kept in mind, as illustrated by our patient.

Horner syndrome combined with ipsilateral upper limb pain and weakness of the muscles of the hand also complies with the diagnostic criteria for Pancoast syndrome, suggestive of a malignant tumor in the apex of the lung affecting both the sympathetic trunk and the inferior trunks of the brachial plexus. Pulmonary pathology was excluded by chest X-ray. The subsequent ENG with a normal SAP in the medial cutaneous antebrachial nerve was compatible with a supraganglionic root lesion as later confirmed by MRI. In case of a Pancoast tumor with involvement of the lower brachial plexus, the ENG would be expected to reveal a decreased or absent SAP.

Our patient experienced onset of Horner syndrome and ipsilateral upper limb symptoms shortly after chiropractic treatment, suggesting the cervico-thoracic manipulation as the cause of or at least worsening factor in the T1-T2 disc herniation. Approximately 33%–50% of patients with a symptomatic thoracic disc herniation report a history of recent trauma,⁹ including torsion and athletic activity. Furthermore, several examples of disc herniations following chiropractic treatment have been reported.¹⁰

Pharmacologic pupillary testing can be utilized both to confirm the presence of Horner syndrome and to locate the lesion in the oculosympathetic pathway. Cocaine is a norepinephrine reuptake inhibitor and will fail to induce pupillary mydriasis if applied topically to a patient with disrupted sympathetic innervation of the iris dilator muscle, confirming Horner syndrome, irrespective of where the lesion is located. Topical hydroxyamphetamine, on the other hand, produces pupillary dilation by releasing norepinephrine from the presynaptic terminal. This effect will only occur if the postganglionic (third-order) neuron is intact, and may therefore be used to differentiate central and preganglionic from postganglionic lesions.¹

Central Horner syndrome due to a brainstem stroke, i.e., Wallenberg syndrome, will rarely be confused with a peripheral cause due to concomitant and characteristic clinical findings consistent with brainstem pathology, including nystagmus, dissociated loss of sensibility, and ipsilateral cerebellar symptoms.

Though considered extremely rare, Horner syndrome, and more specifically partial Horner syndrome, can occur due to an isolated herniated intervertebral disc at the T1-T2 level. The condition may result in diagnostic challenges, including considerations involving carotid artery lesions and malignant pulmonary pathologies.

While the definite pathophysiologic mechanism in our patient remains unclear, it seems evident that manipulations as a minimum altered the configuration of an already existing disc protrusion.