Nontuberculous mycobacterial keratitis

Introduction to non-tuberculous mycobacterial keratitis Non-tuberculous mycobacterial keratitis is a chronic inflammation caused by non-tuberculous mycobacteria (NTM) with multifocal infiltration of the corneal stroma. basic knowledge The proportion of illness: 0.005% Susceptible people: no special people Mode of infection: non-infectious Complications: bacterial corneal ulcers corneal ulcers

Non-tuberculous mycobacterial keratitis

(1) Causes of the disease

Non-tuberculous mycobacteria (NTM) belongs to aerobic bacilli and is widely distributed in the natural environment. Because it has the characteristics of positive acid-fast staining, it is also called acid-fast bacteria. NTM can cause many diseases in humans, including neck. Lymph node inflammation, corneal infection, lung disease and skin ulcers, etc., the infection caused by the bacteria has increased in recent years. According to the biological characteristics of NTM (mainly colony pigments and growth rate), Runyon divides them into 4 groups. The NTMs that cause corneal infection belong to Group IV (rapid growth NTM), among which Mycobacterium fortuitum and Mycobacterium fuliginea are the most common, and non-tuberculous mycobacteria can become a nosocomial infection because it can contaminate reagents and irrigation fluids in hospitals. One of the most common bacteria, most NTM keratitis is associated with corneal surgery, trauma and wearing contact lenses.

(two) pathogenesis

The fatty acids and glycolipids on the NTM cell wall allow it to escape the phagocytic clearance and survive in the tissue for a long time. The relative hypoxia of the corneal stroma makes the NTM dormant without causing disease, but when the body's resistance is reduced or partially used In the case of hormones, the NTM in the dormant state can be transferred to the proliferative phase at any time. It is found that the proliferative cycle of NTM is long and the growth is slow, generally about 20 hours. Therefore, the clinical incubation period of NTM keratitis is long, the pathogenesis is slow, and it can be in a sustained state. According to modern immunology, NTM keratitis is a disease that occurs in an immune disorder. Bacteria cause the imbalance of the cornea's immune balance and progress toward a pathological immune response.

Non-tuberculous mycobacterial keratitis prevention

Prevent corneal trauma and prevent long-term local hormonal application.

Non-tuberculous mycobacterial keratitis complications Complications bacterial corneal ulcer corneal ulcer

Corneal ulcers, perforations, and anterior chamber empyema are common.

Non-tuberculous mycobacterial keratitis symptoms common symptoms tearing corneal burns photophobia abscess eye pain

NTM keratitis is slow onset, and the lesions tend to be delayed. The early symptoms are photophobia, tearing, and redness. Some patients have eye pain, but it is not obvious. As the disease progresses, vision loss will occur. Typical clinical signs include corneal stroma. Focal point infiltration, painless corneal ulcer and matrix abscess; corneal perforation can occur in a small number of patients; satellite lesions and anterior chamber empyema appear in advanced stages.

Non-tuberculous mycobacterial keratitis examination

1. Commonly used examination methods in the laboratory include smear microscopy, culture and animal experiment smear acid-fast staining microscopy (Figure 2) can provide a preliminary laboratory diagnosis for the clinic, its advantages are simple, fast, but sensitive The lower the degree, the sensitivity of the smear after fluorescent staining with auramine-rhodamine, the sensitivity is obviously improved. For the corneal ulcer, the ulcer tissue can be directly scraped for acid-fast staining microscopy and culture; In patients with subvalvular infiltration after LASIK, the corneal flap should be opened for smear and culture. The NTM culture time is longer than that of common bacteria. The judgment result generally takes 7 to 60 days. The commonly used medium has Roche medium, Middlebrook 7H9, 10 , 11 medium or Tween egg protein liquid medium, in addition, molecular biology techniques (mainly PCR technology) can quickly, sensitively and specifically diagnose NTM.

2. Bacteriological examination: For patients suspected of NTM lung disease, sputum smear can be taken for acid-fast staining, sputum culture, and bronchial lavage specimen culture, such as acid-fast staining, should be identified after culture, such as 2 to 3 times. The same NTM can be used to diagnose cerebrospinal fluid, blood or bone marrow in patients with NTM meningitis and blood-borne disseminated NTM.

3. Molecular biological examination: PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of NPS 16S-23 SrDNA gene spacer sequence (IGS) was used for NTM strain identification. Compared with morphological and biochemical routine methods, identification is more accurate, fast and simple.

4. Pathological examination: NTM infection of skin soft tissue, NTM lymphadenitis can be performed for histopathological examination, pathological features of NTM lymphadenitis are granulomatous inflammation, and tuberculous nodules formed by epithelial cells and Langhans giant cells are rare. Without central cheese-like necrosis.

Mantoux skin test: Mycobacterium tuberculosis and NTM have a common antigen. Although the PPD skin test can produce cross-reaction, there are still differences. The PPD-T of M. tuberculosis and the PPD-NTM of NTM are simultaneously tested for skin. NTM patients generally do not have a diameter of more than 15 mm for PPD-T induration. If the diameter of the PPD-NTM skin test is 5 mm or more than the PPD-T skin test, it can be considered as NTM infection.

Diagnosis and identification of non-tuberculous mycobacterial keratitis

According to the clinical manifestations, the clinical diagnosis of NTM keratitis can be made, and the cause diagnosis must rely on laboratory tests.

Differential diagnosis

Some patients may show small linear opacity ("glassy-like" appearance) in the corneal stroma at the early stage of infection, and gradually develop into a matrix annular infiltration, coin-shaped keratitis, and infective crystal-like keratopathy, when the corneal lesions are linear or Dendritic, accompanied by epithelial corneal ulcer should be distinguished from herpes simplex keratitis; for painless corneal ulcer and corneal abscess should be differentiated from anaerobic and fungal corneal ulcer, the identification is mainly based on clinical manifestations And laboratory inspection.

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