Sir,

We welcome the article by Davagnanam et al1 and agree when Horner syndrome (HS) presents with localizing clinical signs the choice of imaging is straight forward. However, the authors could have perhaps done more to focus on isolated HS. While recognizing that isolated HS is an important physical sign, the clinician’s dilemma is deciding whether to scan, when to scan, and what to scan.

We recently presented2 the results of a 5-year retrospective consecutive series of HS cases at our regional neuroscience centre. Seventy-five (74 unilateral and 1 bilateral) cases, with a mean age of 49.7 years (SD ±17 years, range 18–87 years), were identified from the electronic radiology card system and a case note review was carried out. Two cases were recurrent, and both episodes were recorded as one case. Forty-seven cases were clinically isolated, of these the commonest aetiology was undetermined cases (n=22) followed by carotid dissection (n=11).

Positive aetiology was found in four isolated HS cases who had no history of trauma or surgery, no reported headache, neck ache, or pain: two carotid dissections, one pancoast tumour, and one C1 benign aneurysmal boney cyst. Our main concern is, if a HS is only reviewed at 6 weeks as suggested by the algorithm, instead of undergoing prompt imaging, patients with carotid dissection are at significant risk of a ischaemic event (transient ischaemic attack or stroke) within the first 31 days of onset of symptoms.3

Positive aetiology was found in three isolated HS cases who presented with history of greater than 1 year: two had carotid dissection and one a cervical sympathetic paraganglioma. Although we accept that no treatment would be warranted for the dissections at over 12 months, two recurrent cases of carotid dissection were found within our cohort. This highlights the importance of investigating the patient to fully inform them and clinician in the event HS recurs.

These findings suggest that an atraumatic non-painful isolated HS or a chronic history of isolated HS should not be treated as benign entities. We would recommend prompt imaging in all cases. As suggested by Al-Moosa and Eggenberger,4 a prospective study is required to provide evidence to determine what is the ‘gold standard’ imaging modality for isolated HS.