Somnolence syndrome after cranial irradiation : a literature review

Somnolence syndrome is a commonly seen, early-delayed side effect of radiation treatment to the brain. Despite being a recognised side effect for over 30 years, many associated aspects of the syndrome are still unclear, such as which patients are most prone to the condition, what are its associated symptoms, what is its aetiology, what treatment factors affect it and how can it be managed? Literature has shown that somnolence syndrome can occur in children and adults after receiving cranial irradiation. The syndrome is characterised by a variety of symptoms, including mild drowsiness to extreme exhaustion, low-grade fever, nausea, anorexia and headache. Symptoms generally appear between five to six weeks after the completion of treatment. Why and how the syndrome comes about is still uncertain. Popular theory suggests that it is due to transient demyelination of the nerve fibre. The condition has been shown to appear at doses as low as 12 Gy and up to 54 Gy with a fraction size dependence not yet established. The use of steroid therapy has proven to be an effective method to reduce the occurrence of somnolence syndrome in patients receiving cranial irradiation, with the optimal regime still to be determined. Health care professionals should acknowledge and warn their patients of the syndrome, ensuring proper care is available if it develops. Further study is required on the aetiology of the syndrome, the late neurological outcomes of the syndrome and the optimal steroid schedule for its management.