Clinical diagnosis
Case 85
【Progress】Sputum test revealed positive Guffky scale 2+ (G5), indicating active pulmonary tuberculosis. She was transported to the expert hospital for treating tuberculosis because of needing isolation.
【Discussion】
When mycobacterium tuberculosis (tbc) bacilli infect to alveoli, they are engulfed by macrophages but some of them can survive in macrophages, lay dormant and begin to infect. The mechanism of tbc bacilli surviving in macrophages relies upon the specific cell wall with rich lipid which resist or tolerate to liposomes from macrophages and antibiotics. Further, tbc bacilli evolve to get nutrients from lipid of the host. Namely, tricarboxylic acid cycle (TCA cycle) of tbc bacilli gets ATP from host fatty acids to produce their cell walls, inducing exhaustion and weight loss of the host, resulting in the breakdown of the immune system. Tbc symptoms usually take time, months to years to initiate. However, in the situation of tbc bacilli infection under compromising immune system such as AIDS, anti-immune agents and/or steroid hormone, old age, dysfunctions of macrophages and T cell lead to the more active form of tbc infection, miliary tbc (1, 2).
Miliary tuberculosis is mainly caused by initial infection of pulmonary tbc followed by invasion to systemic vein via two routes; from lymphatic channel of hilar node and mediastinal node to venous angle drainage: direct invasion to pulmonary vein at alveolar wall. Under the healthy immune condition, macrophages engulf tbc bacilli and play a role to block the invasion to vessels. However, under a compromising immune condition, tbc bacilli surpass the immune system and expand to systemic organs. When immune system is weakened by AIDS or corticosteroids, immunosuppressive and cytotoxic agents, miliary tbc can develop in cases of not merely initial infection but also of secondary infection after immune acquisition to tbc.
The size of tbc bacilli is 2 to 4μm which is smaller than that of erythrocytes of 7μm, and the smallest size of capillaries is 5-10 μm, implying tbc bacilli migrate all systemic small vessels and stay at the sites of the abundant capillary network present at lung (miliary tbc), bone (causing paralysis), joints, kidney, reproductive organ, peritoneum (peritonitis), pericardium (pericarditis), choroidal membrane of the eye, meninge (meningitis) and skin. The lung owns 700 million alveoli, and the size of each alveolus is 200 μm, producing 70 m2 of surface area, the largest capillary network, which indicates miliary tuberculosis is predominantly found in the lung (3-5).
Clinical manifestations of pulmonary tbc include that lateral chest radiograph (especially retro-cardiac space) might be better to explore minute nodules, leukopenia (decrease of white blood cells and lymphocytes) in laboratory test. Miliary nodules are granuloma which is formed by macrophages surrounding tbc bacilli and then it takes weeks for miliary nodules to appear radiographically after tbc bacilli dissemination (1, 2).
In our case, the patient is high-aged woman with possible impaired immune system,the count of white blood cells was less than 2000/mm3. Although lateral chest radiography was not taken, posterior to anterior radiograph and chest CT showed a number of miliary nodules in the whole lung.
【Summary】
We present a seventy eight-year-old female with miliary tuberculosis which was shown in chest radiograph and CT. Laboratory test revealed leukocytopenia and lymphocytopenia. We should keep in mind that primary infection of occurs in any site and tbc bacilli are engulfed but survive in macrophages and evolve the energy of TCA cycle from host fatty acid. Tbc bacilli spread to via pulmonary vein at the alveolar wall and/or venous angle communicating with lymphatic channel. Miliary tuberculoma is formed by cell-mediated response of macrophages surrounding tbc bacilli.
【References】
1.Sharma SK, et al. Miliary tuberculosis: new insights into an old disease. Lancet Infect Dis. 2005 Jul;5(7):415-30.
2.Curvo-SemedoL, et al. Tuberculosis of the chest. Eur J Radiol2005; 55(2):158–172. Crossref, Medline
3.AndreuJ, et al. Radiological manifestations of pulmonary tuberculosis. Eur J Radiol2004;51(2):139–149. Crossref, Medline
4.WoodringJH, et al. Update: the radiographic features of pulmonary tuberculosis. AJR Am J Roentgenol1986;146(3):497–506. Crossref, Medline
5.McAdamsHP, et al. Radiological manifestations of pulmonary tuberculosis. Radiol Clin North Am1995;33(4):655–678. Medline
2017.12.20