Certain features
may be present which support a diagnosis of infection:
- Most
important feature is necrosis, but less so if the "necrosis" is no more
than some degenerative change in collagen.
- If the necrotic center contains
neutrophils, the index of suspicion for infection should be especially
high .
Pathologists should search for fungal
infection.
- Most necrotizing granulomas are related
to infection.
-
Special Stains: In a few cases the organisms may be visible
on the H & E stained section. Special stains like Ziehl - Neelsen (ZN)
stain for microbacteria and Grocott’s Methenamine Silver
(GMS) stain for fungi.
Grocott’s Methenamine Silver (GMS):
Advantage
and disadvantage of GMS:
GMS is much more reliable than PAS for
staining fungi. Black/lung debris/pigment are usually
distinguishable by being more heterogenous than fungal spores and may
confuse the picture on the GMS. In this case PAS is
helpful.
- Tissue necrosis and a vasculitis are
commonly seen in infections. [Differential diagnosis:- Pulmonary angiitis / granulomatosis (Wegener’s granulomatosis etc ] . Such
vasculitis is usually non-necrotising, showing mural/intimal
infiltration by lymphocytes and other mononuclear cells.
- In Chronic Granulomatous Disease, an
inherited group of conditions characterized by abnormal phagocytic cell
function, necrotizing granulomas occur with a number of infectious
pathogens.
- Microorganisms are generally found most
frequently in an extracellular location within the debris of the
necrotic granuloma center, and not in the cellular rim.
- In mycobacterial infection,
microorganisms may be relatively few and far between, requiring thorough
searching of one or two adequately stained sections. Despite the higher
index of suspicion and endless staining/searching nothing may be
found.
-
A significant proportion of infectious
granulomas (proven some other way), and almost one third of
radiographically solitary granulomatous lesions, will be negative on
special staining.
Therefore a lack of organisms does not
exclude an infectious etiology.
In such circumstances, the pathologist
can describe the lesion, and convey the suspicion, but indicate
the lack of stainable microorganisms.
- If granulomatous inflammation,
especially in association with necrosis, is found in an otherwise
typical nodular fibrous lesion of silicosis , the index of suspicion of
a complicating mycobacterial infection should be very high.
-
Obviously, in any case, if fresh material
is available (Autopsy,/Open/ Thoracoscopic lung biopsy) , and the
possibility of infection is suspected , tissue should be sent for
microbiological examination for appropriate culture.
Serology, particularly in some of the
fungal infections, may also provide useful information.
Differential
diagnosis and etiology of epitheloid cell granulomatosis of the
lung.Verh
Dtsch Ges Pathol. 2000;84:118-28.
Our knowledge
on epithelioid cell granulomatosis of the lung has been extended
in recent years. New entities have been added, like zirconiosis,
others like tuberculosis, mycobacteriosis and sarcoidosis have
gained new interest, because molecular techniques allowed new
insight into their pathogenesis and a more rapid and
species-specific diagnosis. Experimental work in addition has
added a lot of information about the network of cytokines and
other inflammatory mediators responsible for granuloma formation,
however, our knowledge of this network is still incomplete. Three
types of agents are now known to cause epitheloid cell granulomas:
infectious organisms (bacteria, fungi, and parasites), products of
plants and animals (pollen, sporangia, proteins), and metallic
compounds. In addition there is still a group of epithelioid cell
granulomatoses with unknown etiology. Sarcoidosis, one of these
granulomatosis, has recently elicited an old controversy: By
molecular techniques Mycobacteria and Corynebacterium acnes have
been identified in sarcoid granulomas and a link to the aetiology
of sarcoidosis has been proposed. If these bacteria induce some
cases of sarcoidosis by an allergic mechanism, has still to be
proven.
Anatomopathology
of pulmonary granulomatoses.Rev
Pneumol Clin. 1993;49(6):263-7.
Pulmonary
granulomatosis are lung diseases due to inflammatory lesions with
characteristic histiocyte reactions seen in granulomas often
composed of epithelioid and giant cell formations. There are a
number of pathological entities depending upon whether the
aetiology is infectious or immunologic. The pathologist is asked
to determine the type of reaction and to identify the greatest
number of elements possible for the aetiologic diagnosis.
Pulmonary
sarcoidosis: a mimic of respiratory infection.Semin
Respir Infect. 1995 Sep;10(3):176-86.
Sarcoidosis
is an idiopathic multisystem disorder with several clinical and
roentgenographic features suggestive of respiratory infection. In
the absence of infection, it is characterized by the microscopic
presence of noncaseating epithelioid granuloma in affected
tissues. When present, constitutional symptoms, fever, coughing,
and exertional dyspnea usually develop insidiously, although
occasionally Lofgren's syndrome--the triad of bilateral hilar
adenopathy, erythema nodosum and polyarticular arthritis--may
herald the onset of acute disease. Pulmonary involvement is the
roentgenographic hallmark of sarcoidosis; bilateral hilar
adenopathy is the most common manifestation. However, parenchymal
infiltrates and pleural effusion may occur. Although numerous
bacterial and fungal organisms may mimic the clinical and
roentgenographic features of sarcoidosis, tuberculosis and fungal
infections associated with granulomatous inflammation are the
infectious processes most apt to cause diagnostic confusion.
Several diagnostic clues are available to the clinician confronted
with the consideration of sarcoidosis. Roentgenographic staging of
the disorder (stage 0, normal radiograph; stage I, isolated
bilateral hilar adenopathy; stage II, hilar adenopathy and
parenchymal involvement; stage III, isolated parenchymal
involvement; and stage IV, parenchymal fibrosis) provides a
framework on which a differential diagnosis of likely infectious
agents may be constructed and a history of travel to regions of
endemic fungal infection may further narrow the differential
diagnosis. An unexplained exudative lymphocytic pleural effusion
or CD-4 lymphocyte predominance in bronchoalveolar lavage (BAL)
fluid may also suggest a diagnosis of sarcoidosis. However, the
definitive diagnosis of sarcoidosis is dependent upon the
histological demonstration of noncaseating granuloma and the
exclusion of infection in the appropriate clinical and roentgeno-
graphic setting.
