[Why can it be difficult for clinicians to diagnose acute lyme disease? From physiopathology to diagnosis, via abductive reasoning and Bayes theorem]. / Pourquoi le diagnostic de neuroborréliose aiguë reste-t-il difficile? De la physiopathologie au diagnostic en passant par l'abduction et le théorème de Bayes.

The diagnosis of acute neuroborreliosis may be difficult if it's regarded as a "classical" infectious disease. Through a clinical case, we illustrate the difficulties met and we suggest two ways of reflexion to assist in the diagnosis:--firstly, we explain how the comprehension of the behavior of the pathogen agent, which is similar to a parasitic behavior, can help to choose and interpret the results of additional tests;--secondly, we develop practically the clinical form of Bayes's theorem to demonstrate the interest of a rational Bayesian and abductive approach which should be preferred to the classical hypothetical and deductive reasoning.

Mycobacterium marinum infection causing extensive tissue destruction in a hypoxic COPD patient.

We report a skin Mycobacterium marinum infection presenting as wide ulcerative lesions of the arm (4 cm for the widest) in a hypoxic COPD patient who takes 4 mg methylprednisolone daily and higher doses during exacerbations. Diagnostic delay as well as glucocorticoid use could be responsible for the extension of the lesions. Clinical resolution occurred after three months of antibiotic therapy. Extensive ulcerative lesions are uncommon in Mycobacterium marinum infection in an immunocompetent host. This case emphasizes the potential and unusual harmful effect of long-term glucocorticoid therapy used in obstructive lung disease on the spread of Mycobacterium marinum infection.

[Cervical necrotizing fasciitis arising from dental abscess: a rare clinical observation]. / Fasciite nécrosante cervicale compliquant un abcès dentaire: observation clinique rare.

Necrotizing fasciitis of the head and neck is a rare polymicrobial infection, rapidly progressing with a potentially fatal outcome, without early recognition and treatment. Odontogenic infection spreading to the lower neck or anterior chest is an important clinical feature. CT-scan and MRI can be useful in case of doubt. As the relative mild external clinical signs can mask the severe underlying necrosis, the difference in outcome is due to the rapidity of diagnosis and surgical intervention. Surgery consists of complete debridement of all necrotic tissues, repeated as needed and associated with an early tracheotomy. Antibiotherapy is based on the organisms most frequently involved. Hyperbaric oxygen therapy and vacuum-assisted closure could have a role after initiation of intravenous antibiotics and surgical debridement. We report a case of a 23-year old man with a necrotizing fasciitis from a dental origin, necessitating an extensive and repeated surgery, a tracheotomy and antibiotherapy; he developed severe complications such as multisystem organ failure, pericardial effusion and cardiorespiratory arrest.