Pruritic Vesicular Rash on the Forearm in a 33-Year-Old Female with a History of Nickel Allergy

Case at a Glance

A 33-year-old female with a history of sensitive skin and a known nickel allergy presented with a 5-day history of an intensely pruritic, vesicular rash localized to her forearm. The patient was concerned about scabies due to the intense itch, but the clinical presentation, history, and lack of transmission to her partner pointed towards an alternative diagnosis.

Patient's Story

A 33-year-old female presented with a chief complaint of a new rash on her forearm that had been present for five days. It began as a small patch of bumps and gradually spread. The primary symptom was intense pruritus, which persisted throughout the day and night. The patient was worried about a possible scabies infestation, though she noted that her live-in partner, with whom she shared a bed, was completely asymptomatic.

Initial Assessment

The patient described the lesions as small, slightly raised, and fluid-filled vesicles. She has a history of very sensitive and reactive skin, with known allergies to nickel, cats, and dogs. Although she lives with cats, she had never experienced a similar skin reaction. She could not identify a specific new contact with nickel but mentioned that she regularly attends a gym, where she sweats heavily and is in contact with various metal equipment. She also reported a history of small blisters on her fingers and peeling on her palms, which tend to worsen with heat and perspiration. She had attempted self-treatment with a topical betamethasone-gentamicin cream for a short period before discontinuing it due to uncertainty about its appropriateness. On initial virtual examination via provided photographs, a localized erythematous patch with numerous small, grouped papules and vesicles was observed on one forearm.

The Diagnostic Journey

The differential diagnosis included scabies, allergic contact dermatitis, irritant contact dermatitis, and dyshidrotic eczema (pompholyx), given the vesicular nature and her history of similar lesions on her hands. Scabies was considered less likely due to the localized nature of the rash and the absence of symptoms in her close contact. The confinement of the rash to a single forearm strongly suggested an external trigger. Given her known allergy, allergic contact dermatitis to nickel was the leading hypothesis. The patient's gym routine was a significant clue, as sweat can leach nickel ions from metal alloys in fitness equipment, leading to a reaction at the site of contact. The patient also considered a dietary trigger, noting a recent increase in her consumption of nickel-rich foods like oats, which can sometimes cause a systemic contact dermatitis, although her localized presentation made direct contact the more probable cause.

Final Diagnosis

Probable Allergic Contact Dermatitis, secondary to nickel exposure, exacerbated by hyperhidrosis.

Treatment Plan

The patient was advised to immediately discontinue the use of the combination steroid-antibiotic cream. The recommended course of action was to begin treatment with a mid-potency topical corticosteroid. She was counseled on strict allergen avoidance, including using barriers or covered grips on gym equipment to prevent direct skin contact with metals. The patient was advised to schedule an in-person consultation with her primary care physician for a definitive diagnosis and prescription management.

Outcome and Follow-up

A few days after the initial consultation and upon implementing avoidance measures, the patient reported significant improvement. The rash appeared less erythematous, and the pruritus had substantially decreased. She felt reassured that the condition was not contagious and proceeded to schedule an appointment with her physician for formal evaluation. The clinical course strongly supported the working diagnosis of allergic contact dermatitis.