This is a double-blinded clinical trial of children diagnosed with moderate to severe obstructive sleep apnea (OSA) on a baseline polysomnogram (PSG). Participants will receive a 3-day course of dexamethasone, an oral steroid, or placebo control and undergo two PSGs to assess the efficacy of dexamethasone, as a treatment to manage the severity and symptoms in children with moderate to severe OSA.

Obstructive sleep apnea (OSA) is a common sleep-related breathing disorder affecting neonates to adolescents characterized by intermittent partial and complete upper airway obstruction leading to apneas.

The first line of treatment for OSA in young children is an adenotonsillectomy (AT). However, there are long surgical wait times for ATs, up to 3-6 months after a baseline polysomnogram(PSG). This leaves many children untreated, leading to a higher risk of learning deficits and long-term health effects.

Oral corticosteroids have long been used to treat airway inflammation and reduce inflammation of adenoid and tonsil tissue in-vitro. However, there is a lack of knowledge of oral steroids' efficacy in managing OSA. Additionally, the role of the nasal epithelium and the mechanism of action of dexamethasone role at a molecular level is unknown.

The primary objective is to evaluate the efficacy of Dexamethasone in reducing the severity and symptoms of moderate to severe OSA in children in this proof-of-concept exploratory trial.

Participants will be screened by their baseline PSG, followed by 3 study visits conducted at SickKids. Participants will receive a 3-day course of oral dexamethasone or placebo at their first baseline study visit. During baseline, participants will undergo an otolaryngology assessment, a nasal brushing, and questionnaires. Participants will return 2 to 4 weeks after the intervention to the Hospital for Sick Children for a follow-up study visit which includes a repeat PSG, otolaryngology assessment and questionnaires. If no AT is performed within 6 months, participants will return for a third study visit for a repeat PSG, otolaryngology assessment and questionnaires.

Inclusion Criteria:

• Polysomnogram diagnosed with moderate to severe Obstructive sleep apnea (OAHI >5 events/hour)
• Aged 2-10 years
• Presence of adenotonsillar hypertrophy
• Ability to take oral medication and be willing to adhere to the dosing regimen
• Informed consent provided in accordance with institutional policies

Exclusion Criteria:

• Previous adenotonsillectomy
• Presence of symptoms of an upper respiratory tract infection
• Co-existing central sleep apnea
• Hypertension
• Prior or current evidence for abnormal glucose tolerance
• Contraindication for dexamethasone or components of dexamethasone oral suspension,
• Treatment with nasal or systemic corticosteroids within 4 weeks prior to the intervention
• OSA with associated oxygen desaturations <90% for 2 continuous minutes
• Need for non-invasive ventilation long-term due to underlying disease
• Current systemic fungal infections
• Patients with clinically relevant varicella exposure