The diagnosis of eosinophilic lung disease usually relies on characteristic clinical-imaging features and the demonstration of alveolar eosinophilia, while lung biopsy is generally not necessary. The etiology has practical implications, including interruption of a medicinal or illicit drugs, treatment of infections with parasites or fungi, or smoking cessation. The diagnosis of idiopathic eosinophilic pneumonia is considered only once all known causes of eosinophilia have been excluded, especially medications and infections. Treatment of eosinophilic lung diseases involves oral glucocorticoids in most cases and withdrawal of the offending agent when appropriate. Therapies that specifically target the interleukin-5 axis are increasing used.

While glucocorticoids remain the standard first-line treatment for chronic idiopathic eosinophilic pneumonia (CIEP), the long-term use is marred by significant side effects. This case study explores the effectiveness of mepolizumab, an anti-interleukin‑5 (IL-5) monoclonal antibody, as a novel corticosteroid-free alternative in treating CIEP. A 50-year-old woman presented with a 3-week history of progressive shortness of breath, dry cough and night sweats. The blood tests showed eosinophilia, and chest radiography identified lung consolidations. The CIEP was confirmed, ruling out other conditions through a detailed clinical and bronchoscopic work-up. The patient declined to be treated with systemic glucocorticoids. Treatment with mepolizumab was remarkable for effectively resolving symptoms and improving radiological findings without any prior or concurrent glucocorticoid therapy. Notably, the patient remained relapse-free over a 2-year follow-up, underscoring mepolizumab's efficacy as a corticosteroid-free treatment for CIEP. This case study calls for further research into anti-IL‑5 treatment of rare respiratory conditions.

We present a case where a patient with no significant pulmonary nor autoimmune medical history presents with acute hypoxic respiratory failure and a dry cough that's made worse when conversing. She gets diagnosed with eosinophilic pneumonia after bronchoalveolar lavage (BAL) showed 70% eosinophils while also having labs highly suggestive of primary Sjogren's syndrome (pSS) with an anti-SSA titer of 111.3 U/mL and anti-SSA 52 kD Ab, immunoglobulin (Ig)G >200 U. The initial treatment plan was to start rituximab to target primary Sjogren's syndrome associated interstitial lung disease (pSS-ILD), however after close discussion with pulmonology, it was changed to mepolizumab to target eosinophilic pneumonia. From a diagnostic standpoint, it may be tricky to determine which disease process is driving the symptoms especially when the patient has labs that are convincing for both.

Cryptogenic organizing pneumonia (COP) and idiopathic eosinophilic pneumonia (IEP) are two forms of diffuse interstitial lung diseases (ILD) that lead to a rapid respiratory decline in young patients. Both conditions presented with similar clinical and radiological findings, making a clinical diagnosis challenging. They are both considered diagnoses of exclusion, and the treatment for both conditions is high-dose corticosteroids, leading to a quick recovery. Pathological specimens are often required prior to initiating appropriate treatment, leading to significant delays in appropriate therapy and a poorer prognosis. In this case report, we suggest that clinical pearls can be used to establish either diagnosis earlier, which leads to earlier treatment and better outcomes. Our patient presented with an acute respiratory distress syndrome (ARDS) picture, bilateral interstitial infiltrates with peripheral predominance, eosinophilia, and a negative initial infectious and cardiac workup. Based on these findings, we had a high initial suspicion that either COP or IEP was present. Our patient had a bronchoscopy done and was promptly started on steroid therapy soon after, which led to rapid clinical improvement. Pathological specimens were inconclusive, but the patient continued to improve, thereby confirming the presence of either form of ILD. The patient was subsequently discharged home with oxygen and recommended to follow up with a pulmonologist for further outpatient testing and management.

A peripheral blood eosinophilia of greater than 1.0 × 109 /L is relatively unusual and offers a clue to the underlying diagnosis. In 2003, we established a specialist service to diagnose unexplained eosinophilia. To describe the causes of an eosinophilia in our service and the diagnostic algorithm we developed. Subjects were referred by physician colleagues across a range of specialties and undertook standard investigations following a semi-structured protocol. Data were extracted from a bespoke database. Three hundred and eighty two subjects were referred over a 17-year period. Average age was 54 years and 183 (48%) of subjects were female, with 21 of 25 (84%) females in the idiopathic eosinophilic pneumonia group (p < 0001), 22 of 30 (73%) females in the gastrointestinal disease group (p < .008), but 11 of 37 (30%) females in the eosinophilic granulomatosis with polyangiitis group (p < .04). A diagnosis was assigned after systematic evaluation using a pre-defined algorithm in 361 (94.5%) of cases. Fungal allergy (82 subjects: 21%), parasitic infection (61 subjects: 16%) and severe eosinophilic asthma (50 subjects: 13%) were the three commonest individual diagnoses. Hypereosinophilic syndrome (HES) disease including eosinophilic granulomatosis with polyangiitis (EGPA) accounted for 85 subjects (20%) of which seven subjects (2%) had myeloproliferative disease (M-HES). A high IgE was common, and 79 (91%) of subjects with complete data who had an IgE of ≥1000 IU/L had fungal allergy or parasite infection. The serum tryptase was raised in 44 of 302 (14.5%) of individuals across all diagnostic groups, though none had mastocytosis. A diagnosis of an unexplained eosinophilia can usually be determined using as semi-structured algorithm. Parasitic infection and fungal allergy often with severe eosinophilic asthma were common causes, whereas HES, particularly myeloproliferative, disease was relatively rare.