Mycobacterium avium-intracellulare infection

Mycobacterium avium-intracellulare infection
CT scan of patient with right middle lobe aspiration and Mycobacterium avium infection consistent with Lady Windermere syndrome
Classification and external resources
Specialty
ICD-10	A31.0
ICD-9-CM	031.0
DiseasesDB	29182
eMedicine	med/1532
Patient UK	Mycobacterium avium-intracellulare infection
MeSH	D015270

Mycobacterium avium-intracellulare infection (MAI) is an atypical mycobacterial infection caused by Mycobacterium avium complex. This infection causes respiratory illness in birds, pigs, and humans, especially in immunocompromised people. In the later stages of AIDS it can be very severe. It usually first presents as a persistent cough. It is typically treated with a series of three antibiotics for a period of at least six months.

Mycobacterium avium and M. intracellulare (the M. a. complex - MAC) are saprotrophic organisms present in soil and water; entry into hosts is usually via the gastrointestinal tract, but also can be via the lungs.

MAC can cause fevers, diarrhea, malabsorption, as well as loss of appetite and weight loss, and can disseminate to the bone marrow. Therapy for MAI is typically resistant to standard mycobacterial therapies.

Sources and symptoms

MAC bacteria are common in the environment and cause infection when inhaled or swallowed. Symptoms are reminiscent of tuberculosis (TB), and include fever, fatigue, and weight loss. Many patients will have anemia and neutropenia if bone marrow is involved. Pulmonary involvement is similar to TB, while diarrhea and abdominal pain are associated with gastrointestinal involvement. MAC bacteria should always be considered in a person with HIV infection presenting with diarrhea. Recently, M. avium has been found to deposit and grow in bathroom shower heads from which it may be easily aerosolized and inhaled.

The various subspecies of M. avium are prevalent in different areas:

• M. a. avium (MAA) primarily affects birds, but has also been found in ruminant mammals, especially deer.
• M. a. paratuberculosis (MAP) causes paratuberculosis, or Johne's Disease, and also is usually found in mammals.

MAI is common in immunocompromised individuals, including senior citizens and those suffering from HIV or cystic fibrosis. Bronchiectasis, the bronchial condition which causes unnatural enlargement of the bronchial tubes, is commonly found with MAI infection. Whether the bronchiectasis leads to the MAC infection or is the result of it is not always known.

Mycobacterium avium infection in children

M. avium and M. haemophilum infections in children form a distinct clinical entity, not associated with abnormalities of the immune system. M. avium typically causes unilateral swelling of one of the lymph nodes of the neck. This node is firm at the beginning, but a collarstud abscess is formed eventually, which is a characteristic blue-purple in colour with multiple discharging sinuses. The treatment of choice is surgical excision of the affected lymph nodes, with antibiotic treatment (usually clarithromycin and rifabutin for 18 to 24 months) reserved for those patients who cannot have surgery.

MAC in patients with HIV infection

MAC in patients with HIV disease is theorized to represent recent acquisition rather than latent infection reactivating (which is the case in many other opportunistic infections in immunocompromised patients).

The risk of MAC is inversely related to the patient's CD4 count, and increases significantly when the CD4 count decreases below 50 cells/mm³. Other risk factors for acquisition of MAC infection include using an indoor swimming pool, consumption of raw or partially cooked fish or shellfish, bronchoscopy and treatment with granulocyte stimulating factor.

Disseminated disease was previously the common presentation prior to the advent of highly active antiretroviral therapy (HAART). Today, in regions where HAART is the standard of care, localized disease presentation is more likely. This generally includes a focal lymphadenopathy/lymphadenitis.

AIDS patients are given macrolide antibiotics such as azithromycin for prophylactic treatment.

Diagnosis

Diagnosis can be achieved through blood cultures, or cultures of other bodily fluids such as sputum. Bone marrow culture can often yield an earlier diagnosis, but is usually avoided as an initial diagnostic step because of its invasiveness.

Prophylaxis

Clarithromycin or azithromycin may be used for prophylaxis.

Treatment

Postinfection treatment involves a combination of antituberculosis antibiotics, including rifampicin, rifabutin, ciprofloxacin, amikacin, ethambutol, streptomycin, clarithromycin or azithromycin.

Lady Windermere syndrome

"Lady Windermere syndrome" is one term to describe infection in the lungs due to MAC. It is named after a character in Oscar Wilde's play Lady Windermere's Fan.

In recent years, some have described the eponym as inappropriate, and some have noted that it would have been unlikely that Lady Windermere had the condition to which her name was assigned.

The more commonly used term is Nontuberculous mycobacteria or NTM infection, or Non-tuberculous mycobacterial infection (NMI). There is no evidence that a patient's reluctance to spit has any causal role in NTM infection, the chief reason for the term having been applied to older women presenting with the condition.

Classification

Lady Windermere syndrome is a type of mycobacterial lung infection. Patients with this syndrome experience chronic cough, shortness of breath, fatigue and other less specific symptoms.

Pathophysiology

Mycobacterium avium complex is the most commonly found form of non-tuberculous mycobacteria.

Immunodeficiency is not a requirement for MAI.

Mycobacterium avium complex (MAC) usually affects patients with abnormal lungs or bronchi. However, Candace Baker, Jerome Reich and Richard Johnson describe a series of six patients with MAC infection of the right middle lobe or left lingula who did not have any predisposing lung disorders.

The right middle lobe and left lingula of the lungs are served by bronchi that are oriented downward when a person is in the upright position. As a result, these areas of the lung may be more dependent upon vigorous voluntary expectoration (cough) for clearance of bacteria and secretions.

Since the six patients in their retrospective case series were older females, Reich and Johnson and Baker proposed that patients without a vigorous cough may develop right middle lobe or left lingular infection with MAC. They proposed this syndrome be named Lady Windermere syndrome, after the character Lady Windermere in Oscar Wilde's play Lady Windermere's Fan. However, little research has confirmed this speculative cause.

Diagnosis

The diagnosis requires consistent symptoms with two additional signs:

• Chest X-ray or CT scan showing evidence of right middle lobe (or left lingular lobe) lung infection
• Sputum culture or bronchoalveolar lavage culture demonstrating the infection is caused by MAC

Treatment

NTM infections are usually treated with a three-drug regimen of either clarithromycin or azithromycin, plus rifampicin and ethambutol. Treatment typically lasts at least 12 months.

Literary reference

The original Chest article proposing the existence and pathophysiology of the Lady Windermere syndrome suggested the character Lady Windermere in Oscar Wilde's Victorian-era play Lady Windermere's Fan is a good example of the fastidious behavior believed to cause the syndrome. The article states:

We offer the term, Lady Windermere's Syndrome, from the Victorian-era play, Lady Windermere's Fan, to convey the fastidious behavior hypothesized: "How do you do, Lord Darlington. No, I can't shake hands with you. My hands are all wet with the roses."

Victorian women presumably believed "ladies don't spit," and consequently might have been predisposed to develop lung infection.

Shortly after the Lady Windermere syndrome was proposed, a librarian wrote a letter to the editor of Chest challenging the use of Lady Windermere as the eponymous ancestor of the proposed syndrome. In the play, Lady Windermere is a vivacious young woman, married only two years, who never coughs or displays any other signs of illness. While her avoidance of shaking hands might be interpreted as "fastidiousness", two alternative explanations may be just as probable:

1) Lady Windermere actually is in the midst of arranging flowers and consequently cannot properly greet her guest:

[LADY WINDERMERE is at table R., arranging roses in a blue bowl.]

2) Lady Windermere wishes to discourage the flirtatious advances of her would-be suitor Lord Darlington and cites her wet hands as an excuse to keep him from touching her:

LADY WINDERMERE. Lord Darlington, you annoyed me last night at the Foreign Office. I am afraid you are going to annoy me again. . . .

LORD DARLINGTON. [Takes chair and goes across L.C.] I am quite miserable, Lady Windermere. You must tell me what I did. [Sits down at table L.]

LADY WINDERMERE. Well, you kept paying me elaborate compliments the whole evening.]

The scholars highlight the literary malapropism, but some in the medical community have adopted the term regardless, and peer-reviewed medical journals still sometimes mention the Lady Windermere syndrome, although it is increasingly viewed as a limiting and sexist term for a serious bacterial infection.

See also

• Paratuberculosis