The predominant infectious/inflammatory etiology: the pathogenesis of IPT is elusive. Inflammation in IPT has been attributed to a metabolic disturbance, pulmonary infection, and/or antigen-antibody interaction to an unknown agent[ 7]. Thirty percent of IPT cases are reported to be preceded what is a histiocytoma by recurrent respiratory tract infections. Isolated pathogens include: human herpes virus, epstein barr virus, nocardia, mycoplasma, and actinomycetes[ 4, 12]. Repetitive respiratory insults will call for inflammatory cells to migrate what is a histiocytoma to the insult site. Subsequently over-reactive inflammation results in proliferation and infiltration of inflammatory cells, including lymphocytes, plasma cells, and histiocytes. This could explain the persistent elevation in serum inflammatory biomarkers, as C-reactive protein and erythrocytes sedimentation rate[ 10].
The genetic postulate: ALK gene has been used as a molecular surrogate to what is a histiocytoma differentiate benign IPT from malignant IMT. ALK gene is present on chromosome 2p2. The gene encodes for tyrosine kinase receptors, and the resultant derangement will cause ALK protein over-expression and cell proliferation[ 4]. ALK positivity is only observed in IMT patients. Approximately half of IMT patients stain positive for ALK; yet show a great variation with age[ 8]. In contrast to other tumors that stain positive for ALK, ALK-positive IMT is associated with better prognosis than ALK-negative IMT, as the latter is associated with higher rate of metastasis[ 13].
IPT vs igg4-related diseases: A subset of IPT has been correlated with igg4-related diseases[ 16]. “igg4-related” sclerosing disease, a new disease entity, reflects the presence of abundant igg4-plasma cells in the tissues[ 17, 18]. IgG4 is the least abundant of all igg subclasses, and accounts for less than 6% of the total igg subclasses in the serum[ 19]. Serum igg4 is elevated in certain pathological entities such as what is a histiocytoma atopic dermatitis, pemphigus vulgaris, and sclerosing pancreatitis[ 10]. The igg4-related IPT behaves differently than isolated IPT, as it responds greatly to steroids, precluding the need for surgical resection[ 8]. To confirm the diagnosis of igg4-related pulmonary IPT, histological analysis is needed. A recent study reported the presence of igg4-positive plasma cells in plasma cell granuloma, a type of pulmonary IPT[ 20]. This is contrary to serum igg4 which is not always what is a histiocytoma elevated[ 17]. Obliterative vasculitis also raises the probability of IPT over IMT[ 18]. The ratio of igg4 over igg-positive plasma cells, within tissue specimens, acts as a surrogate for diagnosis of igg4-related IPT. A ratio greater than 50% is usually diagnostic[ 13].
As previously stated, complete resection represents the most favorable and recommended diagnostic and what is a histiocytoma therapeutic approach for pulmonary IPT. Patients who witness disease recurrence or those who do not what is a histiocytoma fit for surgery may rarely benefit from other approaches including what is a histiocytoma corticosteroids, chemo, and/or radiotherapy. Those modalities can also be used as adjuncts to suspected what is a histiocytoma incomplete resection[ 29]. Radiotherapy has little to offer for these slow-growing lesions; hence radiation may cause more damage than cure. Corticosteroids’ use has shown contradictory results, though certain case reports showed complete regression after prolonged treatment[ 12]. Interestingly, many IPT lesions resolve completely after core biopsy. Such paradoxical behavior termed “spontaneous resolution”, is not a well understood phenomenon[ 13]. Methotrexate was used in some cases with modest results[ 30]. Crizotinib, a newly synthesized ALK inhibitor, has been used on a patient with pulmonary IMT, and showed sustained partial response[ 31].
In conclusion, this case, to the best of our knowledge, represents the longest reported follow up in an IPT patient. The absence of symptoms and the relative stability of the what is a histiocytoma lesion, after 10 years, stipulate the natural and the benign behavior of this slowly-growing entity. The true outcome of IPT clearly requires further investigation. Greater capabilities in deciphering the diagnosis and approach to this what is a histiocytoma disease, without relying on en bloc excision, lie on top of these investigations.
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