Coexistence of alopecia areata and fixed drug eruption: An uncommon isotopic phenomenon?

INTRODUCTION

Alopecia areata (AA) and fixed drug eruption (FDE) are distinct dermatological conditions, each with unique etiologies and clinical presentations. The coexistence of these two conditions within the same anatomical location is rare and raises questions about underlying pathophysiological mechanisms. This report explores the case of a 40-year-old man with concurrent AA and FDE in the beard region, presenting a possible example of an isotopic phenomenon.^[1] This phenomenon, defined as the development of a new dermatosis at the site of a previous, unrelated skin lesion, offers insight into the complex interplay between localized immune responses and dermatoses.^[1]

CASE REPORT

A 40-year-old man presented with a 4-day history of a dark-colored round lesion in the beard area, within an hour of taking oral paracetamol for muscular pain. A week prior, he had developed a complete loss of hair over the same area. He gives a history of patchy hair loss over the occipital area of the scalp for 2 months.

Dermatological examination revealed a solitary, well-defined alopecic patch about 4 cm in diameter with a smooth surface and short, broken-off hair at the periphery on the beard area of the face in the left mandibular region. A sharply demarcated, round, indurated dusky violaceous plaque was observed within the alopecic area [Figure 1]. Multiple well-defined round-to-oval patches of hair loss of variable size were seen on the occipital area of the scalp. No abnormality was seen on examination of the mucosa and nails.

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Figure 1:

A sharply demarcated, round, indurated dusky violaceous plaque within the patch of alopecia areata.

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A diagnosis of fixed drug eruption and AA was made, and the patient responded to monthly sessions of intralesional triamcinolone acetonide 10 mg/ml.

DISCUSSION

The isotopic phenomenon has been defined as the appearance of a new skin disease at the site of an unrelated healed skin disease.^[1] It was described in 1985 in two cases of tinea infection developing at the site of healed herpes zoster and was termed an “isoloci response.”^[2,3] The term was amended to isotopic response, as “isotopic” is derived from the Greek prefix “iso” and stem “topos,” meaning same place.^[1,3] Though isotopic response is analogous to the isomorphic response, the latter describes the appearance of the same disease at the site of injury.^[1,3]

The phenomenon has most frequently been reported to occur at the site of healed lesions of herpes zoster.^[1,3] Various hypotheses have been proposed, including “locus minoris resistentiae,” or site of lessened resistance, and the composite theory.^[1,3] Residual changes in innate immunity at the site of the healed dermatosis may result in the localization of the new dermatosis in the area.^[4]

In our case, AA was the primary dermatosis, and fixed drug eruption developed within the same anatomical area. However, both conditions were active simultaneously, and the alopecic patch showed signs of disease activity rather than healing. Therefore, by strict criteria, this case does not fit the classical or expanded definition of an isotopic phenomenon ^[4], which requires the new dermatosis to arise over residual changes left by a healed lesion. Nevertheless, the spatial co-localization of two distinct dermatoses raises interesting questions about localized immune dysregulation and warrants further study.

CONCLUSION

The coexistence of AA and FDE within the same anatomical region represents a rare and intriguing clinical scenario. Although this case does not meet the strict or expanded definitions of an isotopic phenomenon, the localized occurrence of two distinct dermatoses suggests a complex interplay of immune responses. This observation highlights the need for further investigation into the mechanisms underlying such spatial co-localization of skin diseases.