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Dermatopathology Pearls

Some pointers taken from the Dermatopathology RCPA Quality Assurance Programme:

1. Glomus tumour:

It can occur in other places other than the nailbed.
Other variants may be glomangioma, glomangiomyoma and symplastic glomus tumour.
Malignant glomus tumour is a rare entity.
A differential is spiradenoma.

2, Fixed drug eruption:

Composed of a combination of erythema multiforme-like changes, mixed inflammatory infiltrate, and melanophages in the superficial dermis.

Here is a nice explanation on the clinical features.

3. Chondrodermatitis nodularis helicis

Painful nodule typically in the upper part of ear in older males.

4. Naevus cell rests in lymph nodes.

Apparently it is not that uncommon (22% of lymphadenectomies in a large study).

5. Superficial acral fibromyxoma

Circumscribed but non encapsulated lesions, typically at fingers and toes.
Strongly CD34 positive.
Differentials include:
    1. Low grade fibromyxoid sarcoma: Deep soft tissue lesion, rarely in digits, no or limited CD34 positivity, strongly MUC4 positive.
    2. Myxoid dermatofibrosarcoma protuberans: Extremely rare at acral site, typically shows areas of conventional patterns of growth and infiltration.

6. Lichen striatus

Involves both the dermal epidermal junction and perieccrine areas.
Differential: lichen planus: does not involve the eccrine glands.

7. Spiradenocyllindroma

A combination of both spiradenoma and cyllindroma.
Brooke- Spiegler Syndrome is associated with spiradenocyllindroma, and also multiple tricoepitheliomas typically on the central portion of the face.  It is an autosomal dominant condition and associated with abnormality of CYLD tumour suppressor gene on chromosome 1q.

8. Dermatofibroma with follicular induction

Dermatofibroma with follicular or sebaceous induction is actually quite common, comprising of 40% of dermatofibromas.
It is characterized by presence of unquivocal papillary mesenchymal body and a sebaceous component.
Any shave biopsies suggestive of basal cell carcinoma must be scrutinized to rule out dermatofibroma.
Dermatofibrosarcoma protuberans rarely present with follicular induction.

9. Sarcomatoid / poorly differentiated squamous cell carcinoma

Part of differential diagnosis of poorly differentiated dermal spindle cell malignancy with surface ulceration at the surface of the skin.  Others include melanoma, atypical fibroxanthoma.

10. Giant cell tumour of tendon sheath.

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