Acute interstitial pneumonia J84.

Idiopathic interstitial pneumonia (IIP).

Acute interstitial pneumonia (AIP) is very rare and accounts for only about 1% of all idiopathic interstitial pneumonia.

It can affect both adults and children. The average age is about 50 years. In children, the clinical picture is observed only extremely rarely.

Men and women are equally affected.

A cause is not yet known. The only striking fact is that primarily healthy people are affected.

The AIP initially shows prodromies such as:

- unspecific symptoms of a virus infection

- Myalgias

- Athralgium

A severe clinical picture then develops suddenly, which is very similar to ARDS (acute respiratory distress syndrome):

- fever

- Shortness of breath

- tracheal cough

- a rapid respiratory failure of the lungs

Auscultation

The auscultation result is - at least initially - bland. Sclerosiphonia may occur in the further course of the disease.

Radiologically and histopathologically the disease progresses in 3 stages:

- acute exudative phase

- proliferative phase

- fibrotic remodelling phase

X-rays: The radiological changes are initially diffusely distributed and in the course of time center in the dependent areas dorsally and basally. These diffuse shadows show a rapidly progressive progression. Pleural effusions are often found on both sides.

HRCT: Symmetrical areas on both sides with milky glass-like infiltrations up to consolidations which are mainly distributed subpleurally.

In phase 1, alveolar edema and hemorrhages with necrosis of type I pneumocytes are found.

In the 2nd phase hyaline membranes form and there is a proliferation of pneumocytes type II. Furthermore, we find a proliferation of myofibroblasts and an increased collagen formation.

In phase 3 the typical fibrotic remodelling takes place, if the patients experience this phase at all.

Patients are usually admitted to the intensive care unit under an ARDS image. X-ray thorax and HRCT are trend-setting.

However, a lung biopsy is a prerequisite for the actual confirmation of the diagnosis.

To exclude other diseases (see differential diagnoses) it is also recommended:

• Sonography of the pleural effusions
• Doppler echocardiography to exclude left heart failure
• BAL to exclude an infectious genesis

• ARDS

• Cardiac pulmonary oedema

• Diffuse alveolar hemorrhage

• Alveolar proteinosis

• Pneumocystis-jirovecii pneumonia

• Bronchoalveolar carcinoma (usually shows a slower development)

Purely supportive measures, since there is no assured drug treatment.

Intensive medical care is mandatory.

Often patients are already ventilated at the time of diagnosis. Non-invasive ventilation is primarily recommended here, as otherwise the high ventilation pressure and the high inspiratory oxygen concentration will probably accelerate the disease.

After exclusion of all important differential diagnoses, an attempt should be made to treat the disease with high-dose steroids, although a reliable therapy has not yet been found:

- 2 x 500 mg prednisolonefor 5 days

- then 1 x 500 mg prednisolone for 3 days

- then 1 x 250 mg prednisolone for 3 days

The further procedure should then be decided on the basis of the course of events.

As a precautionary measure, the simultaneous administration of an antimycotic under high-dose immunosuppression is recommended

- e.g. Fluconazole and an additional antibiotic, primarily a second-generation cephalosporin

- e.g. cefuroxime 3 x 1,5 g/d i.v. plus macrolide

- e.g. erythromycin 3 - 4 x 1 g/d i.v.

The lethality rate of > 60 % is very high. Patients usually die within the first 6 months after the diagnosis is known.

In the survivors relapses are described, which are then mostly terminating.

However, there are also patients who survive the disease. In these patients a pronounced irreversible fibrotic parenchymal remodeling is observed, which is difficult to differentiate from the picture of an IPF.

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