Introduction

The Mycobacterium avium complex (MAC) is a bacterial group that causes MAC lung disease.^1,2 This illness is a form of infection caused by nontuberculous mycobacteria (NTM).¹ NTM are common environmental microorganisms that are naturally present in soil, water, and dust.^1,2 Nearly 80% of lung illnesses in the US are caused by MAC, and there are around 200 species of NTM. MAC lung disease is not communicable, unlike tuberculosis (TB), which is caused by the Mycobacterium tuberculosis bacteria and can be transmitted from person to person.^1,3 Despite daily exposure to NTM, the majority of people do not get infected.¹ All ages and genders can be affected by MAC lung disease; however, some groups are more vulnerable to a slow-growing infection after MAC enters their airway.¹ The most vulnerable are women who have experienced menopause and those over 65.¹ Smoking, a compromised immune system, or pre-existing lung problems are other important risk factors. Bronchiectasis, cystic fibrosis, emphysema, chronic obstructive pulmonary disease (COPD), and a history of prior tuberculosis infection are some examples of these lung disorders.^1,3,4 The greatest significant risk factor for MAC infection in non-HIV patients is considered to be those who have underlying pulmonary conditions. The significance of this article is to understand MAC lung disease and to emphasise the clinical importance of early symptom recognition and diagnosis, while focusing on two hallmark symptoms -  coughing and fatigue

Understanding chronic cough in MAC lung disease

Nature of the cough

In patients with MAC lung disease, coughing is usually continuous and chronic. It can be productive or dry, and mucus is frequently present.^1,4,5 Often, symptoms can be vague, leading to delays in diagnosis.¹ Some people may even experience minor, undetectable, or non-respiratory symptoms.¹ Chronic cough has historically been a common symptom of Mycobacterium intracellulare-avium complex-induced chronic lung illness.³ Before being diagnosed, an indolent cough had been present for an average of 25.6 weeks in a group of patients without any predisposing factors.³ 

Immunocompetent MAC patients are less likely to experience fever and hemoptysis than individuals with other respiratory diseases, such as tuberculosis (TB).⁴

Pathophysiology

Dust, soil, and water are all natural habitats for MAC bacteria.^1,3 The bacteria can lodge in the lungs of susceptible people and proliferate slowly over many years, even though the majority of people exposed to these microorganisms do not get sick.¹ Until the condition is diagnosed and treated, this process leads to low-grade inflammation and progressive, irreversible damage to the airways.¹

The onset of bronchiectasis and airway damage is a major contributing factor to the cough and other symptoms of MAC lung disease.^1,2 The infection develops in the small airways and air sacs, leading to chronic inflammation in the less severe form of MAC lung disease, known as nodular bronchiectatic, which is more frequently observed in older, skinny, nonsmoking women.¹ Bronchiectasis, an irreversible dilatation and scarring of the airways, is the outcome of this inflammation.^1,2 Mucus builds up and acts as a nidus for more NTM growth as well as other respiratory pathogens because the injured airways are unable to remove it efficiently. The lingula and right middle lobe are where the nodules and bronchiectasis are most commonly found.¹ The development of cavities, typically in the upper lobes, as a result of increasing lung scarring or fibrosis in the more severe fibrocavitary illness, might eventually result in persistent fibrosis and respiratory failure.²

Additionally, it has been proposed that MAC microbes could enter the body through drinking water and then be aspirated into the respiratory system, especially when GERD, including silent nighttime reflux, occurs.^2,3 Following exposure to ambient aerosols, this reflux and aspiration may also result in localised airway injury, making people more susceptible to MAC-PD.²

Clinical implications

MAC lung disease is a chronic, incapacitating pulmonary disorder that can have a substantial influence on a patient's quality of life due to its persistent cough and other symptoms.⁵ In addition to being part of patient-reported outcome measures for evaluating the impact of the disease, patients frequently report chest discomfort, exhaustion, and shortness of breath.^1,5 Although these particular effects are not covered in the sources cited, a persistent cough can cause social embarrassment and sleep disturbance. However, the overall impact on health-related quality of life is substantial, and from the patient's point of view, its improvement is a crucial indicator of treatment success.⁵

Along with other symptoms, a persistent cough raises the possibility of problems and an infection that gets worse. If left untreated, a chronic NTM pulmonary infection can gradually harm the lungs and reduce lung function.² Serious side effects that individuals may encounter include hemoptysis, or coughing up blood.^1,4 Over an extended length of time, MAC lung disease can occasionally result in respiratory failure and even death. Within five years of being diagnosed with the cavitary form of MAC lung disease, about one in four individuals with compromised immune systems may pass away.¹
Given these ramifications, reducing long-term hazards significantly requires early detection and treatment.¹ In addition to suppressing the illness and halting its course, treatment attempts to improve the patient's everyday functioning and symptoms.⁵ A key component of treating MAC-PD is effective mucus clearance procedures, which can be accomplished with a variety of non-pharmacologic approaches and inhaled drugs.²

Fatigue as a systemic symptom

Description and presentation

• Fatigue in MAC lung disease tends to be experienced as persistent tiredness, and patients may describe it as extreme fatigue
• This symptom, like others associated with MAC lung disease, is often non-specific and can lead to a late diagnosis.¹ Being non-specific, it can easily be blamed on common ailments like ageing, stress, or other chronic diseases frequent in the groups most at risk of MAC-PD (e.g., elderly patients, patients with existing lung disease)^1,2
• Patient-reported outcome measures, such as the Quality of Life-Bronchiectasis (QOL-B) questionnaire, include a vitality domain to specifically measure how often one feels tired, full of energy, and exhausted.⁵ Fatigue is a common symptom, but the QOL-B vitality scale showed 40% of the patients improved by eight or more points after therapy, showing many of them had less fatigue⁵

Mechanisms behind fatigue in MAC

• Chronic inflammation: Low-grade inflammation and progressive, irreversible alterations in the airways are caused by MAC infection.¹ A systemic process, chronic inflammation, can exacerbate generalised weariness and a sense of unwellness
• Anemia: A common laboratory anomaly in patients with disseminated MAC (DMAC), especially those with AIDS, is profound anaemia.³ MAC patients frequently suffer from anaemia, which can necessitate recurrent transfusions.⁴ Fatigue and decreased oxygenation are directly caused by anaemia
• Poor nutrition and wasting: Patients frequently lose weight and lose their appetite,^1,3 which can result in severe wasting.⁴ Low serum albumin levels (<3.5 g/dL) and a low body mass index (BMI) are markers of severe inflammation and are linked to the advancement of the disease.² The gradual infection can cause severe nutritional impairment, necessitating the need for dietary support^{1, 4}

Impact on daily function

• Decreased physical functioning  activity: People with MAC lung disease frequently have trouble and limitations when it comes to physical activity.⁵ Because of their limited tolerance for exercise, they may require physical therapy programs to increase their endurance and muscular mass.³ Enhancements in physical functioning are significant results of treatment.⁵ Poor physical performance is linked to worse patient outcomes, such as a higher death rate among people with long-term lung conditions⁵
• Psychological effects: Patients with severe MAC lung disease may find it more difficult to engage in activities they once enjoyed, which may result in the emergence of worry or sadness.¹ Patients everyday functioning may be further hindered by cognitive impairments such as memory problems and cognitive fogging, which are included in the NTM symptoms domain of patient-reported outcome measures⁵
• Overall quality of life: One of the most important objectives of treatment for MAC lung disease is to improve overall health-related quality of life (HRQoL) and symptoms, including fatigue.⁵ These improvements are tracked using patient-reported outcome measures such as the vitality scale of the Quality of Life-Bronchiectasis (QOL-B) questionnaire.⁵ A considerable percentage of patients (40%) reported an improvement in fatigue. Although one study did not consistently show average improvements in vitality scores.⁵

Diagnostic challenges and misinterpretation of symptoms

Overlap with other respiratory and systemic diseases

Delays in diagnosis are caused by the wide range and frequently non-specific symptoms of MAC lung disease.^1,2 It is possible for some people to have insignificant or mild symptoms, which are often not respiratory.¹ A persistent cough (with or without mucus), exhaustion, low-grade fever, night sweats, dyspnea, inexplicable weight loss, decreased appetite, chest pain, and anxiety are common symptoms that are readily confused with other chronic illnesses or general malaise.¹ MAC infections have a broad differential diagnosis that encompasses diseases such as sarcoidosis, HIV, lymphoma, fungal infections, and hypersensitivity pneumonitis.⁴

It is important to note that the symptoms of MAC lung disease can mimic those of tuberculosis (TB); however, MAC lung disease is not communicable.^1,3 Compared to TB, MAC is less likely to cause fever and hemoptysis.⁴ In clinical practice, ruling out pulmonary tuberculosis is a crucial diagnostic step.⁴ Furthermore, because MAC is a common environmental bacterium that can exist without generating an obvious infection, isolating the organism from a respiratory material does not always confirm sickness.^2,3 It can be challenging to distinguish between an asymptomatic carrier and a progressing illness, often requiring an extended monitoring period.³ 

Importance of comprehensive clinical evaluation

A thorough clinical evaluation that incorporates clinical observations, radiographic imaging, and microbiological confirmation is crucial given these diagnostic complications.^2,4

Imaging (HRCT scan) and sputum cultures

• CT scans and Chest X-rays are essential for identifying the lung abnormalities linked to MAC infection^1,3
• A 'tree-in-bud' pattern, tiny nodules, and bronchiectasis are among the typical changes that can be detected with greater sensitivity using high-resolution computed tomography (HRCT) scans, which are preferred because they produce clearer, more detailed pictures.^2,3,4 Despite being non-specific, these results ought to raise the possibility of an NTM infection.³ Cavitation may not be seen on conventional radiographs, but HRCT can show it³
• For the diagnosis of MAC lung disease to be made with certainty, microbiological isolation is necessary.⁴ Sputum cultures are used in this process to continuously identify MAC proliferation¹

Symptom timeline and medical history

A comprehensive physical examination and in-depth inquiries regarding symptoms and their progression are essential.¹ ATS/IDSA's clinical criteria for diagnosis include compatible radiographic findings, pulmonary symptoms (such as cough, exhaustion, weight loss, dyspnea, hemoptysis, fevers, and night sweats), and the proper exclusion of alternative illnesses.^2,3 The evaluation of underlying illnesses and risk factors for mycobacterial diseases, such as advanced age, compromised immune systems, or pre-existing lung problems, including bronchiectasis, COPD, cystic fibrosis, emphysema, or prior TB infection, should also be part of a thorough medical history.^1,3,4 This evaluation also looks at how well the patient can handle long-term multidrug treatment.⁴

Clinical significance of early recognition

Why timely identification matters

Preventing irreversible lung damage

Low-grade inflammation and progressive, irreversible alterations to the airways are hallmarks of MAC lung disease.¹ The less severe nodular bronchiectatic form can raise the risk of pneumonia and bronchitis if treatment is not received.¹ The development of holes in lung tissue is a feature of the more severe fibrocavitary illness, which, over time, may lead to persistent lung fibrosis and respiratory failure.^1,2 The important thing to remember is that MAC lung disease causes irreversible lung damage, so even after effective therapy, patients may still have respiratory issues.¹ These long-term hazards, which include the possibility of respiratory failure and death, are significantly reduced by early detection and treatment. Impaired lung function can also result from the disease's progression.² Low body mass index (BMI), low serum albumin (<3.5 g/dL), and low BMI specifically indicate severe inflammation and disease advancement. Other risk factors for disease progression include cavitary disease, low BMI, older age, comorbidities, anaemia, hypoalbuminemia, and elevated C-reactive protein or erythrocyte sedimentation rate.^3,5

Reducing the bacterial burden and improving outcomes

The symptoms of MAC lung disease are non-specific, which sometimes causes delays in diagnosis.¹ Smear positive, an independent predictor of radiographic advancement, suggests that this delay may result in a larger bacterial burden.^1,2 Sputum conversion usually happens between 3 to 6 months, and the goal of the treatment is to achieve culture negativity for 12 months.⁴ Untreated patients, however, experience a high rate of advancement; over two to ten years, between 40 and 60 per cent of them will exhibit evidence of clinical and/or radiological deterioration.^3,5

Educating patients and healthcare providers

Mycobacterium avium complex (MAC) lung disease is a condition of underdiagnosed lung disease caused by nonspecific symptoms. The symptoms include chronic cough, fatigue, shortness of breath, low-grade fever, night sweats, unexplained weight loss, anorexia, chest pain, and anxiety. These are mistakenly referred to as other chronic illnesses or nonspecific malaise and might require prolonged observation due to the ubiquitous nature of the organism. A single positive sputum culture for MAC is generally insufficient for diagnosis. MAC lung disease diagnosis involves a global clinical assessment combining clinical presentation, radiographic imaging, and microbiologic documentation by way of sputum or bronchoscopic cultures. The Infectious Diseases Society of America (IDSA) and American Thoracic Society (ATS) guidelines do incorporate some microbiological criteria for diagnosis, wherein at least two positive cultures of different samples or a single positive culture from bronchoscopic specimens are required. Patients with MAC require follow-up X-rays for monitoring disease progression and must be taught to contact their healthcare provider if they develop concerning symptoms.

Summary 

The two main signs of Mycobacterium avium complex (MAC) lung illness are persistent coughing and exhaustion. However, because they are non-specific, these symptoms are frequently underdiagnosed. Diagnostic delays and misdiagnosis of other respiratory and systemic diseases, including TB, bronchitis, and asthma, are common outcomes of this non-specificity. Early detection of MAC lung disease is made more difficult by the fact that some patients may even have minor, undetectable, or non-respiratory symptoms. The widespread diagnostic difficulties highlight the significance of being vigilant in at-risk groups, such as women, older people, people with compromised immune systems, and people with pre-existing lung diseases, including chronic obstructive pulmonary disease (COPD) or bronchiectasis.

For healthcare professionals to recognise the gradual evolution of symptoms, there is a definite need for improved diagnostic awareness and clinical education. Since a thorough clinical evaluation, including High-Resolution Computed Tomography (HRCT) scans and repeated sputum cultures, is necessary for a conclusive diagnosis, it is imperative to promote prompt referrals to pulmonology or infectious disease specialists. To avoid irreparable lung damage and enhance overall patient outcomes, early detection and treatment are essential.