Nowadays,
the number of patients with some kind of immunosupression continues to increase,
much because of greater use of immunosupressors agents in many different contexts: in treatment of cancer,
connective tissue and other autoimmune disorders,
and in prevention of rejection in organ and stem cell transplant recipients.
Acquired immunodeficiency syndrome remains still a important burden,
like some congenital deficiencies.
The immunocomprosided population is at greater risk of developing infectious and non-infectious complications.
The lung is one of the main targets involved in these complications,
infections accounting for 75% of the total,
making an early and accurate diagnosis fundamental in order to avoid associated morbidity and mortallity.
The organisms involved generally don’t represent a big concern for imnunocompetent individuals,
and the kind of infection could be related to the type of immune system dysfunction:
-cellular immunity abnormalities: organisms of the normal flora become opportunistic agents (like Candida spp) or latent infections could reactivate.
-humoral immunity abnormalities: mostly bacterias,
and as dysfunction progresses Gram negative bacterial infections become more common.
-neutrophil dysfunction: mostly bacterias and fungus.
-neutropenia: one of the most important risk factors,
frequently coexisting with other immunity disfunctions.
In case of transplantations,
either solid organ transplantation or haemtopoeic stem cell transplantation (HSCT),
special attention should be taken on the time elapsed from transplantation,
as it represents an important factor to the differential diagnosis.
In the first month of solid organ transplantation,
complications are mostly related to the surgical procedure/intensive care needs and the major cause of infection is hospital-accquired bacterial pneumonia.
Opportunistic agents generally appear between the first and sixth month of transplantation,
the peak of immunosupression.
Immune reconstitution after HSCT plays an important role on the differential diagnosis,
because specific infections and other complications tend to occur in a predictable way during specific time periods.
There are three recognized phases after HSCT:
- neutropenic phase (days 0 – 30): fungal infectios account for 25% to 50% of all pneumonias in allogenic HSCT recipients,
with Aspergillus being the most common pathogen.
Bacterial pneumonias are rare during this phase.
Non-infections complications include: pulmonar oedema,
drug-related complications,
engraftment syndrome and diffuse pulmonar hemorrhage.
- early post-transplantation period (days 31 – 100): infections are the most frequent problem,
particularly by Aspergillus and Cytomegalovirus (CMV).
- late post-transplantation period (> 100): chronic graft vs host disease (GVHD) may rise the risk of opportunistic infections,
because of the need of corticosteroids.
Non-infections complications include: bronchiolitis obliterans and organizing pneumonia.
Conventional radiography remains the manly first imagiologic technique used.
It allows rapid assessment of the presence of a pulmonary infection,
and can also evaluate the existence of non-infections complications.
Because it lacks specificity to differentiate some pleural and pulmonary processes,
and gives little help in determining the causative pathogen,
Computed Tomography (CT) is usually needed to overcome those needs.
Nevertheless,
there is a significant overlap in CT findings related to different infections and individual antigens,
so it remains essential to incorporate the patient’s context to reach na accurate diagnosis.