Mycobacterial Diseases

Infection caused by MTB

About one-third of people throughout the world are infected with MTB

Tuberculous disease develops in approximately 10% of infected individuals

Infection is most commonly diagnosed in the elderly and people with HIV infection

Mortality is extremely uncommon in treated patients

Morbidity depends on the severity and distribution of lesions in individuals with active disease

Males are more often affected than females

Incidence is higher in foreign-born individuals than in individuals born in the United States

Latin Americans, African Americans, and Asians have higher infection rates than Caucasians

Primary infection is more common in young adults in the United States

Typical symptoms include cough, fever, anorexia, fatigue, weight loss, chest pain, and night sweats

Purulent sputum, hemoptysis, and clubbing may be present

Some patients are asymptomatic

Secondary pulmonary TB is detected more often than primary TB

Secondary pulmonary TB:

• –

  Lesions are characteristically located in the apicoposterior aspects of the lungs and can be nodular, cavitary, or infiltrates

• –

  Mediastinal and hilar lymphadenopathy, with or without calcification, and pleural effusions may be evident

Primary pulmonary TB:

• –

  1.0 to 1.5 cm; focus of consolidation most commonly in the lower part of an upper lobe or the upper part of a lower lobe adjacent to the pleura

• –

  Enlarged, infected tracheobronchial lymph nodes may be seen

• –

  The focus of primary infection may not be visible on chest radiograph

Excellent prognosis for most patients, provided treatment guidelines are adhered to and infections are not due to multidrug-resistant strains

Poorer prognosis with multidrug-resistant organisms

Drug therapy decisions are made primarily based on disease presentation and drug sensitivities

Most common presentation is as a necrotizing consolidative process in one or both lung apices

Caseous necrosis is often observed

Cavities, usually located in the upper lobes and often measuring between 3 and 10 cm, may be present

Enlarged, infected tracheobronchial or mediastinal lymph nodes can be seen

Other findings can include:

• –

  Circumscribed nodule, mass, or masses (tuberculoma)

• –

  Miliary TB: innumerable 1- to 3-mm nodules (granulomas) distributed throughout the lungs and other systemic sites

• –

  Primary TB: solitary 1.0- to 1.5-cm nodule with central necrosis, calcification, and/or fibrosis, most often in the lower part of an upper lobe or the upper part of a lower lobe, usually subpleural

• –

  Pleural TB: thickened pleura, sometimes showing discrete granulomas, with effusion

• –

  Bronchopleural fistula

Necrotizing (caseating) and nonnecrotizing granulomas

With chronicity and healing, granulomas undergo fibrosis and calcification

With immunocompromise, less organized histiocytic infiltrates and necrotic areas can be seen

Mycobacteria can often be demonstrated with an acid-fast stain

A negative acid-fast stain does not rule out TB

Some reports of benefits of immunohistochemical stains for detection of MTB

Nucleic acid amplification

DNA sequencing tests

• –

  Used to differentiate MTB from NTM

• –

  Detects mutations that confer drug resistance

• –

  Can be used to strain-type organisms to allow for the determination of specific isolates and assess the spread of disease

Epithelioid cells show highly ruffled interdigitating cell membranes and well-developed endoplasmic reticula and may contain thick-walled mycobacteria and large Golgi complexes

FNA and transbronchial needle aspiration can be very helpful for diagnosis

Infections with NTM, fungi, and Nocardia

GPA

Sarcoidosis

Hypersensitivity pneumonitis

Malakoplakia

Silicotic nodule