Methacholine Challenge Positive Bronchial Hyperresponsiveness

A 26-year-old female law student presents with an 8-week history of chronic cough and episodic chest tightness triggered by exercise, cold air, and strong perfumes. She has a history of childhood atopic dermatitis and allergic rhinitis. Her baseline spirometry is completely normal (FEV1 98% predicted, FEV1/FVC 0.81, negative bronchodilator reversibility). Methacholine challenge testing is performed using doubling doses of methacholine via nebulizer. Her FEV1 drops from 3.08 L at baseline to 2.60 L at 4 mg/mL, with PC20 calculated at 4.0 mg/mL as shown by the marker **A** in the diagram. Which of the following best describes the clinical significance of this result?