A 37-year-old woman presented with papillary thyroid cancer as a complication of prior chest and neck radiation to treat a posterior mediastinal ganglioneuroblastoma, for which the patient underwent surgical resection as a child. The ganglioneuroblastoma obliterated the left second intercostal space and extended into the neck along the sympathetic chain, which was transected during resection, producing postoperative Horner’s syndrome. Additional late-onset complications of radiation treatment included mild aortic stenosis.

Physical exam revealed heterochromia iridis (Fig. 1), ptosis, and anisocoria. The patient also noted the absence of left facial and arm flushing with heat exposure, exercise, or consumption of spicy foods.

Fig. 1
figure 1

The patient’s affected left eye was different in color, with subtle pupil asymmetry and ptosis.

Horner’s syndrome produces the triad of ptosis, miosis, and anhidrosis due to damage to the ipsilateral sympathetic chain. The differential diagnosis is broad but should be driven by patient-specific factors. Congenital or acquired Horner’s syndrome in children can lead to heterochromia iridis.14 Sympathetic stimulation has a trophic effect on iris melanocytes, and denervation impairs melanin pigmentation, making the affected eye lighter.3,57 The patient's unilateral anhidrosis and absence of flushing was consistent with Harlequin syndrome, which is rare but can occur with Horner’s syndrome.8

This case exemplifies multiple complications of pediatric malignancy treatment and highlights the importance of cancer survivorship clinics, in which this patient was enrolled.