More on Atypical Mycobacteris in ORLHNS- Outline of Talk by our Registrar

Non-tuberculous mycobacteria (NTM) have become an increasingly important disease of childhood.

59 — 92% of mycobacterial cervicofacial infections in children are a result of NTM. Mainly affects

children <5 years, with most occurring 16 — 36 months of age. The great majority of children with

NTM are not immunologically impaired. The specific organisms are M. avium—intracellulare (aka

MAC, 70% to 90% of cases), M. kansasii, M. scrofulaceum, M. fortuitum, M. haemophilum, M.

abscessus, M. malmoense. Infection by M. bovis has decreased dramatically with the institution of

milk pasteurization.

These organisms are commonly found in soil, water, dust, aerosols, domestic and wild animals, milk,

and other food items. The portal of entry is believed to be through the mouth, and the tonsils have

been implicated in particular. The predilection for younger children is probably related to their

tendency to put contaminated objects in their mouths. The tendency to present in the winter

months may reflect the greater likelihood of viral upper respiratory infection in this season, which

might allow the causal organism easier access via inflamed mucous membranes. When within the

macrophage, MAC is able to survive within a vacuole and may ultimately use the macrophage as a

launching pad for infection if the host’s defences weaken.

The typical clinical presentation is of a painless, firm, enlarging and persistent neck mass that has

failed to respond to antibiotic therapy in a paediatric patient. The most common site of

mycobacterial infection in the neck is the anterior superior cervical region, followed by the posterior

cervical, middle cervical, supraclavicular, and submental regions. Atypical mycobacterial infection is

not infrequently found in the pre-auricular region. It tends to occur unilaterally. The skin becomes

adherent to the surrounding tissues and develops a characteristic violaceous discoloration. The

infection might progress to fluctuation and the development of a draining sinus. These lesions

generally produce few systemic symptoms. The differential diagnosis should include all diseases

specific to the salivary glands, tuberculous adenitis, infectious mononucleosis, cat-scratch disease,

brucellosis, actinomycosis, nocardiosis, toxoplasmosis, malignancies (especially lymphoma), and

macrocystic lymphatic malformation.

In addition cervical lymphadenitis, NTM may be involved with chronic otitis media (M. avium, M.

fortuitum, M. abscessus), or chronic laryngitis (M. leprae).

FNA carries the risk of fistula formation as does abscess incision and drainage. Mycobacterial

infection is definitively diagnosed by culture. Cultures for atypical mycobacteria may, however, be

negative even when infection is present. Only about 50% of excised diseased lymph nodes will be

culture positive. With a mean time of about eight weeks for culture and twelve weeks for sensitivity

results, initial diagnosis depends greatly on the clinical features. Most atypical mycobacteria elicit

granulomatous inflammation with acid-fast bacilli, and many establish cavitary disease difficult to

distinguish from TB. The histologic findings associated with MAC vary considerably and range from

granulomas to nodular foam cell lesions to purulent and necrotizing inflammations. Mantoux tests

for atypical mycobacteria are available and were at least weakly positive in 95% of cases in the series

by Hawkins and colleagues. NTM-specific antigens have been developed and are reported to be

extremely successful for diagnosis. Newer methods that use polymerase chain reaction techniques

to detect mycobacterial RNA in tissue and M. avium deoxyribonucleic acid in gastric aspirates are

still not widely available. 

Chest x-ray findings are typically absent. Contrast-enhanced CT images show asymmetric cervical lymphadenopathy with contiguous low-density, necrotic, ring-enhancing masses involving the subcutaneous fat and skin. In addition, inflammatory stranding of the subcutaneous fat characteristic of bacterial inflammation is minimal or absent with NTM infection.

The treatment of choice is complete surgical excision of the involved nodes. Medical treatment of

NTM with prolonged courses of antimicrobials is not well established. Hawkins and colleagues

showed resolution of neck masses in 4 of 18 cases of atypical mycobacterial infection with

chemotherapy alone. If excision is incomplete or disease recurs, fluoro-quinolones (e.g.

ciprofloxacin), clarithromycin or azithromycin plus ethambutol with rifampin should be used. If the

parotid gland is affected, a superficial parotidectomy with facial nerve preservation is necessary.

Removal of involved skin is often necessary during excision. Careful attention should be paid to

avoid any injury to the mandibular branch of the facial nerve because it is often adherent to the

tract. Patients with otitis media caused by M abscessus should receive clarithromycin plus an initial

course of amikacin plus cefoxitin. Surgical debridement may be required.