Hypersensitivity Pneumoni...

During second wave of COVID-19(20 MAY 2021), A 46-year-old female presented with dry cough for 7 days, fever and shortness of breath for two days. Fever was 38 to 39 degrees Celsius with no diurnal variation. Shortness of breath was acute in onset with no associated complaints of chest pain, palpitations, orthopnea, or abdominal pain. On examination, she had tachycardia, tachypnea, and hypoxemia with an oxygen saturation of 80% measured by a pulse oximeter on room air. Physical examination revealed diffuse scattered wheezing and crackles on chest auscultation and was otherwise unremarkable. Laboratory examination (complete blood count, serum electrolytes, and renal and liver function tests) was within normal range except for an increased leukocyte count of 12,300 cells/mm³.

Reverse transcription-polymerase chain reaction (RT-PCR) for COVID was negative.

Initially we thaught that it was a case of RTPCR negative COVID-19 pneumonia. patient was managed in the ward with antibiotics (ceftriaxone and azithromycin), steroids and non-invasive ventilation (NIV). 

Methylprednisolone was given to the patient and her condition improved. She was then discharged on a tapering dose of steroids for 2 weeks and advised to follow up.

After 2 month(26 JULY 2021) patient again admitted with similar complaint, On further probing into the history, it was found that she had several pigeons at their home as pets. This time HRCT scan of the chest was done which showed multifocal discrete patches of ground glass opacities, multiple centrilobular nodular opacities and mosaic attenuation.

Methylprednisolone was given to the patient and her condition improved. She was then discharged 32 mg of methylprednisolone and advised to avoid contact from pigeons and follow up.

After 1.5 month XRAY chest PA view was performed which shows resolution of bilateral lung opacities.

After 3 month HRCT thorax was performed which shows resolving mosaic attenuation, and ground glassing in bilateral lung fields.

On the basis of history, clinical examination, and radiological evidences diagnoses of acute hypersensitivity pneumonitis was made.

Chest X-ray images of the patient(20 MAY 2021)On Presentation: 
Ill-defined patchy as well as confluent radio-opacities are seen in the subpleural and peripheral locations in bilateral lung fields at upper and mid zones (left more than right) with perihilar sparing (encircled).

High-resolution CT chest images of the patient at two different CT cuts(26 July 2021)
Figure (A): Multiple centrilobular nodular opacities (red arrow) coalescing to form patches of consolidation
Figure (B): Multiple centrilobular nodular opacities (red arrow)
Both (A) and (B): multifocal discrete patches of ground glass opacities with intervening areas of normal lung parenchyma giving mosaic attenuation appearance

Chest X-ray images of the patient(10 SEPTEMBER 2021)
Resolution of pathology with steroids treatment and avoidance of exposure.
High-resolution CT chest after three months follow-up at two different CT cuts(2 NOVEMBER 2021)
Both (A) and (B) show resolving mosaic attenuation, and ground glassing in bilateral lung fields.

What is the probable diagnosis?