Spiny Keratoderma With Exceptionally Large Hyperkeratotic Lesions

Dear Editors,

1.

Spiny keratoderma (SpK) is an uncommon subtype of punctate palmoplantar keratoderma (PPPK) characterized by numerous small, firm, filiform keratotic projections on the palms and soles [1]. We report an extreme, decades‐long case with unusually large palmoplantar spines clinically mimicking a tree‐man phenotype, yet it was consistent with SpK on clinicopathological correlation.

An 80‐year‐old man presented with numerous yellow, hyperkeratotic protrusions on the palms, soles, and volar digits. The lesions extended to the lateral margins but spared the dorsal surfaces. Lesions measured 3–30 mm, and several plantar lesions elevated the nail plate (Figure 1a–e). The lesions first appeared as 1–2 mm spines at age 10, and gradually increased in size and number over 70 years. No relatives were known to have similar lesions. His medical history included hypertension and ischemic stroke, without arsenic exposure, systemic disease, or malignancy.

FIGURE 1.

Clinical and histological findings. (a–e): numerous yellow, firm, hyperkeratotic protrusions measuring 3–30 mm on the palms, soles, and volar digits, extending to the lateral margins while sparing of the dorsal surfaces. (f) Low‐power view showing a localized, cup‐shaped epidermal depression surmounted by a sharply‐demarcated keratotic column. (g) High‐power view of the boxed area in (f) demonstrating a column of parakeratosis with underlying hypogranulosis; no koilocytosis or dyskeratosis is observed. (h, i) Immunohistochemical staining for cytokeratin 5/6 demonstrates strong positivity predominantly in the basal layer of the epidermis, supporting a keratinocytic origin.

Histopathology revealed a localized, cup‐shaped epidermal depression surmounted by a well‐demarcated column of hyperkeratosis with parakeratosis and underlying hypogranulosis. No koilocytosis or dyskeratosis was observed (Figure 1f,g). Immunohistochemistry using an anti‐human papillomavirus (HPV) monoclonal antibody (clone K1H8) was negative, and HPV DNA was not detected by polymerase chain reaction. Computed tomography showed no malignancy. Based on clinicopathologic correlation, SpK was diagnosed. Management consisted of keratolytics and shaving. Reported treatments for SpK include keratolytics (e.g., salicylic acid and urea), retinoids, and mechanical or surgical approaches; however, recurrence is common and efficacy is variable [2].

The differential diagnosis included type 1 PPPK (Buschke–Fischer–Brauer disease), arsenical keratosis, porokeratosis palmaris et plantaris disseminata (PPPD), and verrucae. The striking horn‐like morphology raised concern for extensive HPV–driven disease, including the phenotype referred to as tree‐man syndrome; however, this was excluded by histopathology and negative HPV studies [3]. Type 1 PPPK was excluded by the presence of parakeratosis with hypogranulosis, rather than compact orthokeratosis with hypergranulosis [1]. Arsenical keratosis was unlikely given the absence of characteristic histopathologic features and a compatible exposure history [4], whereas porokeratosis variants, including PPPD, were excluded due to the absence of dyskeratotic changes or vacuolar degeneration [2].

SpK has been reported in hereditary and sporadic forms; hereditary cases typically present during adolescence and early adulthood [5], whereas sporadic cases occur later in life and have occasionally been associated with internal malignancy [2]. Although no family history was identified in our case, a hereditary etiology cannot be excluded, as de novo mutations or reduced penetrance may obscure familial patterns. Genetic testing was not performed due to the patient's preference. Immunohistochemistry demonstrated cytokeratin 5/6 positivity (Figure 1h,i); however, detailed keratin profiling was not available, limiting further assessment of epidermal differentiation. Lesions in SpK are typically small and not known to enlarge markedly over time. Mechanical stimulation or gradual coalescence may have contributed to lesion enlargement, although neither was strongly supported in our case. The prolonged clinical course may therefore have contributed to the progressive enlargement. Additional cases are needed to determine whether this represents an extreme long‐term presentation of SpK or a distinct clinicopathologic subtype within the spectrum of SpK.

Ethics Statement

The authors have nothing to report.

Consent

Written informed consent was obtained from the patient for publication of this report and accompanying images.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data available from the corresponding author upon reasonable request.