Dermatology MCQ - Inflammatory Dermatoses - Chronic superficial scaly dermatitis

A 60-year-old man presents with a 5-year history of slowly progressing, asymptomatic, red-brown, finely scaly patches on his trunk and proximal extremities. The lesions are slightly atrophic and do not respond to topical antifungal creams. On diascopy, the scale is easily detached, and a characteristic reddish-brown background is revealed. What is the most likely diagnosis?

A. Psoriasis
B. Tinea Corporis
C. Mycosis Fungoides
D. Chronic Superficial Scaly Dermatitis (Parapsoriasis)
E. Pityriasis Rosea

Correct Answer: D. Chronic Superficial Scaly Dermatitis (Parapsoriasis)

Explanation:

• The presentation is classic for Chronic Superficial Scaly Dermatitis (CSSD), also historically and commonly known as small plaque parapsoriasis. The key features are its chronic, asymptomatic course, the morphology of "digitately" or "fingerprint-like" arranged, red-brown, fine, "branny" scaly patches on the trunk and extremities, and the characteristic "cigarette-paper" atrophy or wrinkling upon close inspection. The finding on diascopy (pressing a glass slide against the skin) that reveals a reddish-brown background after the scale is removed is a helpful clinical clue.

• Why the other options are incorrect:

  • A. Psoriasis: Psoriatic plaques are typically thick, silvery-white, and adherent (Auspitz sign may be present). They are rarely atrophic and are usually symptomatic (pruritic). The morphology and chronic, asymptomatic nature are not consistent with psoriasis.

  • B. Tinea Corporis: This fungal infection presents as annular, expanding plaques with a raised, scaly, and often vesicular border. It is usually pruritic and responds to antifungal treatment, which failed in this case. The distribution and morphology of CSSD are not annular.

  • C. Mycosis Fungoides: This is the most important differential diagnosis, as early patches of Mycosis Fungoides (MF) can be indistinguishable from CSSD. However, classic CSSD lesions are typically more superficial, have a finer scale, and are more uniform and stable over many years. The diagnosis of CSSD is often one of exclusion after considering and ruling out MF. The stability over 5 years without progression to plaques or tumors favors CSSD, but a biopsy is often warranted to distinguish them.

  • E. Pityriasis Rosea: This is an acute, self-limiting eruption that resolves within 6-12 weeks, characterized by a herald patch and a Christmas-tree distribution on the trunk. The 5-year history definitively rules this out.

Key Points for Exams

• Clinical Variants: The two main types of "parapsoriasis" are:

  1. Small Plaque Parapsoriasis (SPP): Synonymous with CSSD. Lesions are typically <5 cm.

  2. Large Plaque Parapsoriasis (LPP): Lesions are >5 cm, often more irregular, and have a higher risk of progression to Mycosis Fungoides (cutaneous T-cell lymphoma).

• Relationship to Mycosis Fungoides: This is the critical exam point. SPP/CSSD is considered a benign condition with no significant potential for malignant transformation. In contrast, LPP is now often viewed as the earliest stage of Mycosis Fungoides and requires careful long-term monitoring.

• Prognosis: CSSD is benign, chronic, and persists for decades with minimal change. It is often asymptomatic and does not affect general health.

• Management:

  1. Emollients: To relieve dryness.

  2. Topical Corticosteroids: Low-potency steroids may mildly improve the appearance but are often ineffective.

  3. Phototherapy: The most effective treatment. Narrowband UVB or PUVA can lead to significant clearance or remission of the lesions, although they often recur after treatment cessation.

  4. Monitoring: For classic SPP/CSSD, reassurance and periodic review are sufficient. A skin biopsy is frequently performed at least once to rule out early MF.