Thanks to everyone for their opinion and feedback, very helpful. An opportunity kind of made my mind up for me as a fellow on Canuck Audio was selling a VSi75 with a set of KT120' and KT150's with only a 100 hours on both. Statistical analysis and graphical representations of data were performed with GraphPad Prism (version 6.0 c) and SPSS (version 22) for MAC OS X. For all variables, variance homogeneity and Gaussianity were tested with Bartlett and Kolmogorov-Smirnov tests, and we proceeded with parametric tests as our PET and clinical data were normally.
Pulmonary Mycobacterium avium complex (MAC) infection is a type of non-tuberculous mycobacterial (NTM) infection. It is relatively common and continues to pose significant therapeutic challenges. In addition, the role of MAC in pulmonary pathology remains controversial in many instances.
MAC infections often occur in patients with a pre-existing pulmonary disease or those with depressed immunity. However, it is also seen frequently in otherwise healthy patients, with a predilection for older women who deliberately suppress the cough reflex (Lady Windermere syndrome) 1-3.
A number of patient groups have been associated with increased risk of pulmonary MAC. They include 2,3:
Isolation of MAC from a patient's lung is not pathognomonic of infection, as colonization is common, and thus microbiology needs to be correlated with clinical and radiographic appearances 2,3.
Pulmonary MAC infection is typically insidious, with a chronic cough usually productive of purulent sputum being most common. Hemoptysis and constitutional symptoms are not typical 2.
Mycobacterium avium and Mycobacterium intracellulare are now considered together, and referred to as Mycobacterium avium complex (MAC) or Mycobacterium avium-intracellulare complex (MAIC). They cannot be distinguished on the grounds of human pathologic manifestation or imaging features, and are treated similarly, although M. avium has a predilection for chickens whereas M. intracellulare prefers rabbits 2,3.
They are ubiquitous organisms, found in both fresh and salt water, but do not tend to cause human disease. Patients with MAC infection, unlike those with pulmonary tuberculosis, are not contagious 2.
Three main forms of pulmonary MAC infections are recognized 3,5,6:
In upper lobe cavitary form, thin-walled cavities with overall volume loss and fibrosis are the dominant feature, often also with features of endobronchial spread with tree-in-bud opacities seen elsewhere.
In the nodular or non-classic manifestation, the dominant feature is bronchiectasis with associated centrilobular nodules. Unlike pulmonary tuberculosis, there is no predilection for the upper lobes. In elderly white females, the right middle lobe and lingula are particularly affected.
Bronchiectasis, seen as tram-track opacities and ring shadows, may be evident. Patchy airspace opacities are also common. Pleural effusions are uncommon 2. Upper zone cavities may also be seen with associated volume loss and scarring 3.
The most common findings of MAC infections include 1,2:
Many treatment regimes have been published, with no clear gold-standard evident, although as is the case with pulmonary TB, multi-drug therapy is ideal to avoid resistance 2.
In patients who are unable to tolerate medical management, and who have an adequate respiratory reserve, resection of affected portions of the lung may be undertaken. Complications of surgery include bronchopleural fistulas, hemoptysis and empyema2.
In patients in whom isolates of MAC are not clearly pathogenic, follow-up is required, keeping in mind that evidence of radiographic progression may take a number of years to be convincing 3.
Prognosis depends on the form of the disease. In the upper lobe cavitary form, lung destruction is usually progressive and can lead to respiratory failure and death if successful treatment is not instituted.
In patients with the nodular bronchiectatic form (Lady Windermere syndrome) the disease is much more indolent, however, eventually, this form may also lead to enough parenchymal damage to result in respiratory failure and death 3.
The underlying pulmonary abnormality (e.g. COPD, pneumoconiosis) may dominate the radiographic appearance.