Treating The Acute Onset Of An Asymptomatic Solitary Blister

M. Joel Morse, DPM

A 68-year-old Caucasian female presented to the office with acute onset of a solitary, asymptomatic, spontaneous, tense blister of three days’ duration on the lateral aspect of the right great toe.

   She is active and plays a lot of tennis. However, there was no history of trauma or friction from footwear prior to the eruption, and she never had anything such as this blister appear. There is no history of photosensitivity and the patient cannot recall any new drug intake in the preceding couple of weeks. The patient had visited a nail salon two days prior for nail care and polish. She remembers that she felt a prick when the nail technician was working on the great toe but thought nothing of it.

   The dermatological exam revealed a 3.5 cm x 1.3 cm tense solitary bullae on the fibular aspect of the left hallux. It is a tense, non-tender blister on a non-erythematous base. No erythema is present around the base and there is no pain at the toe. Prior to the formation of the blister, the patient did not have any itching or any redness in the area.

   Her history includes insulin-dependent diabetes for 30 years and the recent incorporation of an insulin pump to help manage her diabetes. There is a history of osteoarthritis, back problems, epilepsy, heart disease, hypertension and sinus problems. She notes meticulous foot hygiene and denies any history of calluses, corns or ulcers. Her most recent HbA1c was 6.4 and the fasting blood sugar on the morning of the appointment is 69, which is somewhat low. The rest of the past medical history is noncontributory.

Key Questions To Consider

1. What are the characteristics of this condition?
2. What is the most likely diagnosis?
3. What is your differential diagnosis?
4. What was a key to making the diagnosis?
5. What complications can arise from this condition?

Answering The Key Diagnostic Questions

1. A 3.5 cm x 1.3 cm tense solitary bullae on the fibular aspect of the left hallux as well as a tense, non-tender blister on a non-erythematous base
2. Bullosis diabeticorum
3. Blister beetle dermatitis, insect bite reaction, friction blisters (mechanical trauma), contact dermatitis, vesicular tinea pedis, dyshidrotic eczema (pompholyx), blistering distal dactylitis, bullous fixed drug reactions, bullous pemphigoid, bullous systematic lupus erythematosus, epidermolysis bullosa acquisita, bullous impetigo and bullous erythema multiforme
4. A biopsy of the involved skin revealing a subepidermal bulla without any inflammatory infiltrate as well as a negative direct immunofluorescence test
5. Secondary infection can occur if the bulla ruptures go untreated.

What The Exams Revealed

The physical exam showed that despite a 30-year history of diabetes, there was no loss of protective sensation (Semmes-Weinstein monofilament 5.07) and no loss of vibratory sensation to all five toes and metatarsal heads bilaterally.

   The vascular status was normal in that she had palpable pulses of the dorsalis pedis and posterior tibial arteries, and there was no dysvascularity to the toes. The orthopedic exam did reveal a mild hallux abducto valgus deformity of the involved foot and a rectus alignment on the left foot. No hammertoe deformities were present.

   A complete set of radiographs did not reveal any pathology to the soft tissues or bone underlying the large bullae. There was no acute fracture, tumor or dislocation present.

   A biopsy of the involved skin showed a subepidermal bulla without any inflammatory infiltrate. A direct immunofluorescence test was negative.

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