Answer to October 2014 Photo Quiz

Abstract

Answer: Imported cutaneous diphtheria. The suspected colonies were rapidly identified as Corynebacterium diphtheriae by use of a Microflex LT matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometer (Bruker Daltonics, Bremen, Germany) and subsequently characterized as nontoxigenic Corynebacterium diphtheriae biotype mitis by the National Reference Center for Corynebacterium of the diphtheriae Complex (Institut Pasteur, Paris, France). Treatment with antibiotics was carried on for a total duration of 14 days and allowed for a complete recovery. Nasopharyngeal swabs were taken for all members of the household (i.e., the patient's sister, father, and mother) in order to assess the presence of asymptomatic carriers. All samples were negative for C. diphtheriae growth. Multilocus sequence typing of the isolate generated a new allelic profile, assigned as sequence type 251 (1). Diphtheria is usually considered a life-threatening pharyngitis or laryngitis, and C. diphtheriae is generally not regarded as a skin pathogen. In vaccinated countries, cutaneous diphtheria is discovered as imported cases in travelers coming from areas where the disease is endemic or as autochthonous cases in socioeconomically disadvantaged populations (2,–4). Clinical presentation of skin diphtheria is nonspecific, and most commonly, the organs involved are the lower and upper limbs. Clinical symptoms typically begin as a vesicle, which rapidly progresses to form a punch-out ulcer. At first, these skin lesions may be painful, but they rapidly become insensitive to pain. Diphtheria ulcers generally evolve chronically, and spontaneous recovery can take several weeks. Interestingly, in the present case, the lesions were pruriginous, and scratching them could therefore enhance the diffusion of the bacterium. Definitive diagnosis is generally provided by culture of lesion swabs, but the specific Tinsdale medium is generally not available, as it is expensive and has a shelf life of 1 week. C. diphtheriae colonies are morphologically indistinguishable from those of other Corynebacterium species and thus are likely to be confused with skin flora. Furthermore, most ulcers yield growth of associated pathogens such as Staphylococcus aureus and Streptococcus pyogenes, therefore implying the existence of a causal relationship between the latter pathogens and the skin lesions (5, 6). In fact, these pathogens are usually involved in acute skin infections (e.g., erysipelas or impetigo), while cutaneous diphtheria is chronic and painless. C. diphtheriae identification is challenging and time-consuming with the use of conventional methods, but as it proved to be of valuable assistance in this investigation, MALDI-TOF mass spectrometry would probably simplify and expedite the identification of this pathogen (7, 8). Recommended treatment of skin diphtheria includes thorough cleaning of the lesion, penicillin or macrolide therapy, and, in cases of toxigenic symptoms, antitoxin (2, 9, 10). In conclusion, chronic cutaneous ulcers in specific epidemiological situations should be tested for diphtheria, independent of vaccination status. Their singular clinical and microbiological manifestations probably explain why cutaneous lesions evolve chronically and are more contagious than respiratory infections (3). (See page 3523 in this issue [doi:10.1128/JCM.00779-13] for photo quiz case presentation.)