What Is Blistering Distal Dactylitis (BDD)?
BDD is an infection caused by a bacteria called group A beta-hemolytic Streptococcus (GABHS), although there have been reports of group B Streptococcus, Staphylococcus aureus (SA) also causing BDD. The symptoms manifest as medium to large non-tender blisters at the distal end of the fingers. Children from the age of two years to sixteen years are commonly affected; however, it has also been reported in immunocompromised adults, like those suffering from diabetes and AIDS (acquired immunodeficiency syndrome).
The blister seen in BDD is often single but can be on multiple occasions; it is oval and measures around ten millimeters to thirty millimeters. A blister of this size is referred to as bulla. The bulla in BDD sits on an erythematous (reddish) base and is filled with seropurulent (combination of serous and purulent) fluid. As the lesion progresses, it will eventually erode along with the surrounding skin, which can cause pain and tenderness. The lesions are known to resolve on their own, but in individuals with severe immunodeficiency, they have been known to progress to underlying tissue and bone, often requiring amputation.
What Causes Blistering Distal Dactylitis (BDD)?
Hays and Mullard first reported BDD in 1972. They believed nose-picking to be the cause of infection, which is plausible because the affected individuals were mostly children and tended to pick their noses.
It is now believed that any reservoir of bacteria can be a source of infection. The most common being insect bites, erosions, traumatic cuts, burns, etc. The actual pathogenesis of GABHS-induced BDD is unclear. Still, in the case of a Staphylococcus aureus infection, it is believed that the bacteria secrete toxins that split the epidermis, through which the discharge oozes out as a blister.
It is important to note that clinically, differentiating BDD caused by GABHS and Staphylococcus aureus is impossible. The only way to diagnose the exact organism is through gram staining and cultures. Gram staining involves the use of crystal violet or methylene blue as the primary color to stain the bacteria, and cultures are done to identify the type of organism causing the condition.
How Is Blistering Distal Dactylitis (BDD) Diagnosed?
The blisters seen in BDD often greatly resemble the lesions seen in conditions like herpetic whitlow (an infection caused by herpes simplex virus), bullous impetigo (bacterial skin infection), epidermolysis bullosa simplex (a skin condition caused due to genetic alterations), etc. Therefore, the final diagnosis is not based on just physical examination.
Gram staining, a laboratory procedure, helps determine the BDD. However, it is important to know that BDD and bullous impetigo are caused by bacteria (Staphylococcus and Streptococcus) which can be misleading.
A definitive diagnosis is reached through a detailed history, physical examination of the blister, laboratory investigations, and looking for the below-mentioned signs to eliminate differential diagnosis.
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BDD differs from herpetic whitlow in appearance; the latter has a more herpetic appearance, with white (usually pus) filled blisters, whereas pus is seldom found in the bulla of BDD.
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Herpes simplex virus (HSV) is responsible for herpetic whitlow which can be diagnosed with the help of a Tzanck smear that will show viral cytopathic effects or through a polymerase chain reaction (PCR) which will detect the presence of HSV.
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It is important to note that both herpetic whitlow and BDD can coexist in the same affected infant because both conditions have been known to be caused by thumbsucking, which is common in children.
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Another way of differentiating them is to treat the blisters with antibiotics; symptoms of BDD tend to subside, whereas those of herpetic whitlow blisters remain unphased (because a virus causes them).
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BDD also resembles frictional blisters and can be distinguished by the appearance of a bland bulla that occurs at the site of the friction, unlike BDD blisters which are erythematous and occur at the tips of the digits.
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Blisters caused due to thermal and chemical burns, and insect bites can be easily differentiated from BDD with the help of a detailed history.
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The blisters in bullous impetigo are superficial and fragile to those seen in BDD.
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Other blistering disorders like epidermolysis bullosa simplex (EBS), which is a chronic complex genetic condition, and localized bullous pemphigoid (BP) can be differentiated from BDD (an acute infectious condition) with the help of physical examination and direct immunofluorescence respectively.
How Is Blistering Distal Dactylitis (BDD) Treated?
Usually, the condition is limited and resolves over days; a few cases where it evolved into an abscess or cellulitis has been reported. To prevent this, it is best to treat the patient with oral antibiotics after the initial diagnosis itself.
Recently, it has been reported that BDD can also cause methicillin-resistant Staphylococcus aureus (MRSA). A new protocol has been established to cover all the possible organisms causing BDD (GABHS, BP, and MRSA). The protocol includes the following drugs-
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Trimethoprim/Sulfamethoxazole - Always given to patients with MRSA-positive BDD patients, the recommended dose for children below 40 kilograms is 40 milligrams/kilogram of Sulfamethoxazole and 8 milligrams/kilogram of Trimethoprim for 24 hours, given in two divided doses every 12 hours for ten days. Vancomycin can also be used for MRSA-positive cases.
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Amoxicillin/Clavulanate Potassium (Augmentin) - This is the preferred drug for BDD caused by MRSA or BP. The recommended dosage is 90 milligrams/kilogram/day, divided every twelve hours, and administered for ten days.
Apart from the above-mentioned oral antibiotics, a few popular choices include intravenous Vancomycin (for MRSA-positive BDD), Flucloxacillin, Dicloxacillin, and Cloxacillin for Penicillin-resistant Staphylococcus aureus. Surgical management of BDD involves:
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Incision and drainage of the bulla.
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Wet-to-dry compress to dry the eroded areas.
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A course of antibiotics.
Conclusion:
BDD is a bacterial infection caused by different strains of bacteria like MRSA, SA, and GABHS. It is commonly seen in children and immunocompromised adults and often occurs in conjunction with other bacterial infections of the eyes, gastrointestinal tract, upper respiratory tract, or genitourinary tract. Symptoms include blisters which often mimic those seen in conditions like EBS, BP, and herpetic whitlow. Diagnosis is made with the help of a detailed history, physical examination, and necessary investigations and treatment involving the administration of antibiotics and surgery (if necessary).
