In recent years, an increase has been observed in the isolation of microorganisms from the Mycobacteriaceae family such as Mycobacterium malmoense. These mycobacteria can cause both extrapulmonary and pulmonary disease, and are clinically relevant in 70–80% of patients with pulmonary disease.1 We need to determine the presence or absence of disease based on agreed criteria,2 taking into account that such disease generally occurs in immunosuppressed individuals with general or local immunodeficiency. There are case series in which it has been isolated in patients with cystic fibrosis, prior tuberculosis, pneumoconiosis3 and Crohn’s disease, but we present the case of a patient without underlying illness with pulmonary disease caused by M. malmoense.
A 45-year-old female smoker (15 cigarettes per day) with 23 pack years of cumulative tobacco use, with no other history. She was seen for chronic bronchitis, right pleuritic pain over the last year, and, in recent months, uncomplicated respiratory infections. A chest X-ray was ordered, which showed evidence of pulmonary infiltrate with cavitation in the right apex, which was not present on an earlier X-ray performed eight years earlier. The study was expanded with a chest CT which revealed the presence of nodular opacities, some with cavitation in the right upper lobe (RUL) (Fig. 1). A microbiological study in sputum was also ordered; bacilloscopies were negative, but M. malmoense was isolated in two determinations in the culture, and was also isolated in bronchoalveolar lavage.
Chest CT: radiological findings suggestive of post-primary tuberculosis with involvement of apical and posterior segments of the RUL, traction bronchiectasis and bilateral centrilobular emphysema predominantly in the upper lobes. (A) Major cavitation of 36 mm associated with pleuroparenchymal scarring. (B) Multiple heterogeneous nodular opacities.
The diagnostic guidelines of the American Thoracic Society (ATS)2 and the British Thoracic Society (BTS) were reviewed, and based on microbiological, clinical and radiological criteria, the pathogenic nature of M. malmoense was evaluated and the decision made to begin treatment with azithromycin, rifampicin and ethambutol. No sensitivity study was performed due to the limited value in this case. The patient was informed of the possible adverse effects of the treatment and received advice on stopping smoking.
In follow-up visits at three and six months, the patient reported adequate tolerance of the treatment and that she was asymptomatic. Subsequent sputum bacilloscopies and mycobacteria cultures converted to negative at one month from the start of treatment, remaining so in subsequent monthly follow-ups. Likewise, an improvement was observed in the chest CT ordered at six months. Spirometry was performed, showing mild peripheral airway obstruction, with a negative bronchodilator test, thus ruling out the presence of chronic obstructive pulmonary disease at that time (forced vital capacity [FVC] 3,130 ml [110%], maximum expiratory volume in the first second of forced expiration [FEV1] 2380 ml (98%), FEV1/VC 74.85%, maximal mid-expiratory flow [MMEF] 75/25 1910 ml [57%]).
In view of the results, it was decided to maintain the treatment for one year, based on the BTS recommendations.2M. malmoense is an environmental mycobacterium that generally does not cause disease in humans and human-to-human transmission has not been described.
Infections of this type are more common in other environments, such as northern Europe, although its isolation is becoming increasingly common here due to the increase in cases in Spain in recent years.4 There are few reported cases of M. malmoense, the prevalence of which varies widely from country to country, with the highest figures in northern Europe, although over the years new cases of disease have appeared, with the first case in South Korea described in 2015 and the twelfth in France in 2017.5
Pulmonary infection due to M. malmoense is difficult to diagnose.6M. malmoense has been shown to have a greater tendency to present major cavities and air-fluid levels in comparison with M. tuberculosis,7 although these differences are not sufficient for diagnosis. Some studies have found a higher prevalence in males, with a mean age of 58 years, with infection limited to the upper lobes in some 30% of cases.8
It is necessary to tailor the treatment in each case, as no single established regimen exists. A review published in 2016 suggested treating with isoniazid, rifampicin and ethambutol, with or without fluoroquinolones/macrolides9, for at least 12 months after sputum cultures have become negative.
The growing detection of these mycobacteria compels us to think of them as disease-causing agents. Increasingly, studies are being conducted such as that by Vande Weygaerde et al.,10 but we cannot forget that the difficulty of diagnosing diseases caused by M. malmoense and other non-tuberculous mycobacteria lies in the cross-cutting interpretation of microbiological, radiological and clinical data.
Please cite this article as: Gámiz-Molina AB, Martín-Ripoll L, Cassini-Gómez de Cádiz LF, Gallardo-Medina M. Mycobacterium malmoense: cuando lo raro empieza a dejar de serlo. Enferm Infecc Microbiol Clin. 2021;39:476–477.
