Clinical Manifestations of Nontuberculous Mycobacterial (NTM) Infections

Overview

• NTM infections display distinct clinical patterns: immunocompetent individuals usually develop pulmonary disease characterized by chronic cough and bronchiectasis, whereas patients with severe immunosuppression (CD4 < 50 cells/µL) develop disseminated disease with fever, night sweats, and multi‑organ involvement. 1

Pulmonary Disease in Immunocompetent Patients

Common Symptoms

• Chronic or recurring cough is present in virtually all patients with NTM pulmonary disease. 2

Radiographic Phenotypes

Fibrocavitary disease

• Thin‑walled cavities with minimal surrounding parenchymal opacity, limited bronchogenic spread but prominent contiguous spread, and marked pleural involvement; it predominantly occurs in patients with pre‑existing structural lung disease such as COPD, bronchiectasis, prior tuberculosis, or pneumoconiosis. [2][3]

Nodular/bronchiectatic disease

• Mid‑ and lower‑lung field abnormalities with multifocal bronchiectasis on HRCT in up to 90 % of cases; it mainly affects post‑menopausal women of slender habitus and is associated with morphotypes such as scoliosis, pectus excavatum, and mitral‑valve prolapse. [2][3]

Physical Examination

• Auscultation may reveal nonspecific findings including rhonchi, crackles, wheezes, or “squeaks” reflecting underlying airway disease. 2

Disseminated NTM in Patients with Advanced HIV/AIDS

Risk Thresholds

• Disseminated NTM occurs almost exclusively when CD4 counts fall below 50 cells/µL, with a median presentation CD4 < 25 cells/µL. 1
• In the pre‑antiretroviral era, approximately 40 % of individuals with CD4 < 10 cells/µL developed disseminated NTM within one year. 1

Etiology

• Mycobacterium avium complex (MAC) accounts for about 90 % of disseminated NTM cases in AIDS patients. 1

Clinical Presentation

• Laboratory abnormalities (severe anemia with hematocrit < 25 %, elevated alkaline phosphatase, and elevated lactate dehydrogenase) typically appear 1–2 months before bacteremia. 1

Physical Findings

• Abdominal tenderness or hepatosplenomegaly is common, whereas palpable lymphadenopathy is uncommon in disseminated MAC. 1

Organ Involvement

• Autopsy series demonstrate involvement of most internal organs even when no localizing symptoms are present. [1][4]
• Pulmonary involvement is rare, occurring in only ~2.5 % of AIDS patients with disseminated MAC. [1][4]
• Isolation of MAC from respiratory samples in HIV patients usually reflects colonization or early dissemination rather than active lung disease. 4

Immune Reconstitution Inflammatory Syndrome (IRIS)

• IRIS can develop after initiation of antiretroviral therapy; the most frequent manifestation is suppurative lymphadenopathy (painful cervical, axillary, or inguinal nodes). Other manifestations include pulmonary infiltrates, soft‑tissue abscesses, and skin lesions, often accompanied by fever without the full MAC bacteremia syndrome. 4

Disseminated NTM in Non‑AIDS Immunocompromised Hosts

At‑Risk Populations

• Renal or cardiac transplant recipients, chronic corticosteroid users, patients with leukemia, and individuals with rare genetic defects of the IFN‑γ/IL‑12 pathway. 1

Typical Presentations

• MAC – most often presents as fever of unknown origin. 1
• Rapidly growing mycobacteria (M. chelonae, M. abscessus) – commonly cause multiple subcutaneous nodules or draining abscesses; they are the predominant species in non‑AIDS disseminated disease. [1][5]

Extrapulmonary Localized Infections

Cervical Lymphadenitis (Children)

• The most common NTM disease in children aged 1–5 years, affecting submandibular, submaxillary, cervical, or pre‑auricular nodes; ≈80 % of culture‑proven cases are due to MAC, and it is rare in adults without HIV infection. 4

Skin and Soft‑Tissue Infections

• Occur at sites of puncture wounds, surgical incisions, or trauma; M. chelonae is the most frequently reported cause of LASIK‑associated keratitis. Lesions present as localized infections, nodules, or abscesses. 6

Diagnostic Considerations

Common Pitfalls

• Disseminated MAC can mimic tuberculosis; clinicians should not assume TB without appropriate testing. 7
• Detection of MAC in respiratory specimens from HIV patients does not equate to pulmonary disease; it usually indicates colonization or early dissemination and should prompt evaluation for systemic involvement. 4

Recommended Diagnostic Approach

• Blood cultures are diagnostic in >90 % of disseminated MAC cases; a single positive culture suffices for diagnosis. 4
• If two blood cultures are negative in a symptomatic patient, consider bone‑marrow or liver biopsy with culture. 4
• For isolated lymphadenopathy without bacteremia, excisional biopsy of accessible nodes is advised; fine‑needle aspiration may be required for deep adenopathy (intrathoracic, intra‑abdominal, retroperitoneal). 4

Species‑Specific Clinical Patterns

• Pulmonary disease: MAC > M. kansasii > M. abscessus. 2
• Disseminated AIDS: M. avium (dominant MAC species) > M. kansasii. 1
• Disseminated non‑AIDS immunocompromised: M. chelonae and M. abscessus are most common. 1
• Cervical lymphadenitis: MAC accounts for ~80 % of cases, followed by M. scrofulaceum. 4

Important Species Distinctions

• In the United States, M. intracellulare causes the majority of MAC lung disease, whereas M. avium predominates in disseminated MAC among AIDS patients. 1
• M. abscessus can cause pulmonary disease but is not associated with disseminated infection in AIDS. 1
• Species‑level identification is essential because treatment regimens, drug‑susceptibility patterns, and prognosis vary markedly. 8

Bone Marrow Involvement in Disseminated Mycobacterium avium Complex (MAC) in Advanced HIV

Epidemiology & Pathophysiology

• MAC routinely involves the bone marrow in disseminated disease, especially in patients with advanced HIV infection (CD4 < 50 cells/µL); bone‑marrow examination is diagnostically valuable when blood cultures are negative or rapid diagnosis is needed. – CDC recommendation. 9
• Disseminated MAC is a multi‑organ infection that characteristically involves most internal organs, including the bone marrow, in severely immunosuppressed patients. – CDC recommendation. 9

Hematologic Manifestations

• Hematologic abnormalities—anemia, leukopenia, thrombocytopenia, and pancytopenia—are hallmark features of disseminated MAC and reflect bone‑marrow involvement. – Evidence from CDC and the New England Journal of Medicine. [10][9]
• The anemia seen with disseminated MAC is often out of proportion to the stage of HIV disease, serving as a clinical clue to MAC involvement. – CDC recommendation. 9

Diagnostic Approach

• Practical algorithm for suspected disseminated MAC in HIV patients with CD4 < 50 cells/µL: