Hand-limited prurigo with features overlapping brachioradial pruritus and photodermatoses

Introduction

Photodermatoses comprise a heterogeneous group of disorders, including polymorphic light eruption, actinic prurigo, chronic actinic dermatitis, and solar urticaria.¹ Brachioradial pruritus (BRP) is a chronic neuropathic itch condition affecting the dorsolateral upper extremities, typically associated with cervical nerve compression; chronic ultraviolet (UV) exposure has also been implicated in its pathogenesis.2, 3, 4 Here, we report a case of photodermatosis presenting with prurigo nodularis localized to the sun-exposed dorsal hands, associated with mild central cervical canal stenosis, that responded to nemolizumab.

Case presentation

A 76-year-old Asian man presented with a 3-year history of pruritic skin lesions on the dorsal hands and forehead. The patient initially experienced spontaneous pruritus, followed by the development of cutaneous eruptions. Although treatment with topical corticosteroids provided slight relief of pruritus, the skin lesions did not improve. He was a motorcycle delivery driver for approximately 20 years, with reduced occupational exposure in recent years because of age. He had no significant past medical history. Physical examination revealed multiple clustered, firm, hyperkeratotic brownish nodules with excoriations on the bilateral dorsal hands. In addition, well-demarcated, erythematous small patches were observed on both upper sides of the forehead (Fig 1, A-C). The patient reported intermittent episodes of moderate-to-severe pruritus, with a Worst Itch Numerical Rating Scale of 6.5.

Fig 1.

Clinical features at the initial presentation. A and B, Multiple clustered, firm, hyperkeratotic brownish nodules on the bilateral dorsal hands. Left, A; Right, B. C, Well-demarcated erythematous small patches on the upper forehead.

A biopsy was obtained from a nodule on the left dorsal hand. Histopathologic examination revealed marked hyperkeratosis and acanthosis. The papillary dermis showed upward projection, with perivascular infiltration predominantly composed of lymphocytes, admixed with a small number of histiocytes, while eosinophils were scarcely observed (Fig 2, A and B). Immunohistochemical staining with antitubulin beta III antibody demonstrated numerous dermal nerve fibers immediately beneath the epidermis, in contrast to normal skin (Fig 2, C and D). Laboratory tests revealed mild renal dysfunction (creatinine 1.58 mg/dL) without eosinophilia or elevated IgE levels. Given the chronic, localized, and treatment-refractory pruritus of the upper extremities, a neuropathic etiology, including BRP, was suspected, and cervical magnetic resonance imaging was performed. Magnetic resonance imaging revealed degenerative disc bulging with C5/6 disc space narrowing and osteophytes with ligamentum flavum hypertrophy at C5/6–C6/7, resulting in thecal sac compression, consistent with central cervical spinal canal stenosis on orthopedic evaluation (Fig 3).

Fig 2.

Histopathologic findings of a nodule on the dorsal hand. A and B, Acanthosis with slight spongiosis. In the papillary dermis, vertically oriented capillaries are observed, and perivascular infiltration of lymphocytes and histiocytes is present throughout the dermis, accompanied by dermal fibrosis (hematoxylin–eosin; original magnification ×40 [A], ×200 [B]). C and D, Numerous tubulin beta III-positive nerve fibers arranged immediately beneath the epidermis (C), compared with normal human skin (D) (visualized using 3,3′-diaminobenzidine; ×200).

Fig 3.

Cervical magnetic resonance imaging findings. Cervical magnetic resonance imaging showing degenerative disc bulging with narrowing of the C5/6 intervertebral disc space, and osteophytes with ligamentum flavum hypertrophy at C5/6–C6/7.

Based on these findings, the patient was diagnosed with prurigo nodularis predominantly affecting sun-exposed areas. The erythematous lesions on the forehead were considered possibly attributable to contact dermatitis or photocontact dermatitis, although no apparent contact allergen or relevant exposure could be identified. Pregabalin was added; however, no improvement in the skin lesions was observed. Nemolizumab was then administered at an initial dose of 60 mg, followed by 30 mg 4 weeks later. Pruritus improved markedly after the first administration (Worst Itch Numerical Rating Scale, 1–2). The lesions on the dorsal hands resolved, leaving hypopigmented scarring (Fig 4, A). As the symptoms improved, nemolizumab treatment was discontinued after the third injection. However, 8 weeks after the final dose, following motorcycle delivery work, the patient developed scaly erythematous patches on the face, ears, neck, and dorsal hands. Notably, no prurigo nodules recurred (Fig 4, B-D). The patient was subsequently advised to practice strict photoprotection, including sunscreen use and sun avoidance with protective clothing and a hat. No further exacerbations were reported thereafter.

Fig 4.

Clinical features after treatment and natural sun exposure. A, After the second administration of nemolizumab, the prurigo nodules on the bilateral dorsal hands resolved, leaving hypopigmented scarring. B-D, Eight weeks after the final administration of nemolizumab, following motorcycle delivery work, well-demarcated scaly erythematous patches developed on the face, ears, neck, and dorsal hands. No recurrence of prurigo nodules was observed.

Discussion

Actinic prurigo has been most frequently reported among American Indians, whereas cases in Asian populations are relatively rare and often present with a prurigo nodularis–like phenotype involving sun-exposed areas such as the face, ears, forearms, and dorsal hands.^5,6 Reduced minimal erythema doses to UVA alone or to both UVA and UVB have been reported in patients with actinic prurigo.^6,7 However, standardized phototesting could not be performed because the necessary equipment was not available at our institution, limiting the objective assessment of photosensitivity and further characterization of this photodermatosis.

Nevertheless, erythematous plaques with eczematous changes developed on sun-exposed areas after natural UV exposure, raising the possibility of photodistributed or eczematous dermatoses, including actinic prurigo, chronic actinic dermatitis, photoallergic contact dermatitis, and polymorphic light eruption. The latter typically affects intermittently sun-exposed sites rather than chronically exposed areas such as the face and dorsal hands.⁸ However, the absence of recurrent prurigo nodules following a single episode of UV exposure suggested that UV exposure alone was insufficient to explain the chronic nodular eruption.

In BRP, cervical spinal changes are considered a primary pathogenic factor that may alter itch afferents, while long-term UV exposure has been implicated as an additional contributing factor through peripheral nerve alterations.2, 3, 4^,9 Structural changes in cutaneous innervation, including epidermal nerve fiber sprouting, have been described in both BRP and prurigo nodularis; however, in prurigo nodularis these changes are generally considered secondary to persistent scratching, whereas in BRP they may reflect neuropathic alterations.¹⁰ Although the present findings were located predominantly beneath rather than within the epidermis, the presence of numerous tubulin beta III-positive nerve fibers may suggest remodeling of cutaneous innervation and support a neuropathic contribution.

Clinically, spontaneous pruritus preceded the development of skin lesions. In addition, the lesions were predominantly localized to the dorsal hands, particularly around the bases of the thumb and index finger. In the context of cervical spinal stenosis, this distribution supports a neuropathic contribution. Repeated UV exposure related to his occupation— affecting the face, neck, and ears that remained exposed despite helmet use, as well as the dorsal hands covered only by cotton work gloves while gripping the handlebars—may not only have triggered photosensitivity-related inflammatory responses but also further enhanced or unmasked neuropathic alterations in peripheral cutaneous nerves. The overlap of these factors may explain why prurigo nodules developed exclusively on the dorsal hands. In addition, although no apparent psychiatric comorbidity was identified, the possibility that repetitive habitual scratching contributed to the formation of prurigo nodules cannot be excluded.

The marked clinical response to nemolizumab further supports a role for interleukin-31–mediated neuro–immune interactions in this phenotype. Taken together, this case may represent an interface between neuropathic and photo-induced pruritic processes.

Conflicts of interest

Dr Ugajin has received speaker honoraria from Maruho and Sanofi. Dr Yamamoto-Murata has no conflict of interest to declare.