Breathing pattern disorder masquerading as occupational asthma

Background: Serial peak flow monitoring is commonly used to diagnose occupational asthma (OA). Methods: A laboratory animal (LA) worker presented with work-related dyspnoea triggered by talking, dust and modest exertion. It was also present, to a lesser extent, away from work. She recorded her peak flow (PF) ≥4 times a day on consecutive days for 4 weeks. The values were plotted using specialist software. Results: Spirometry was normal (FEV1 2.98 (105%) and FVC 3.41 (106%)). PF plot showed striking work-related variability (fig 1); OASYS score was 3.91 and ABC score was 95 indicating >90% probability of OA. Serum specific IgE and skin prick tests to LA allergens were negative. There was no exposure to other respiratory sensitisers. Respiratory physiotherapy assessment identified breathing pattern disorder (Nijmegen Questionnaire score 46/64). We explained she did not have OA; her symptoms were managed with physiotherapy and she continued working in her existing role. Conclusions: Whilst serial PF monitoring remains an important tool in diagnosing OA, it is not 100% specific; results must be interpreted alongside the clinical history and, if available, immunology tests. PF measurements can be inaccurate in patients with abnormal breathing pattern and inducible laryngeal obstruction. Clinicians should be aware that such conditions may cause false positive results to avoid misdiagnosis of OA with potentially serious consequences.