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Classification of Photodermatoses & PMLE — 3rd Year Dermatology PG Theory

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PART 1: CLASSIFICATION OF PHOTODERMATOSES

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I. IDIOPATHIC (IMMUNOLOGICALLY-MEDIATED) PHOTODERMATOSES

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II. PHOTOAGGRAVATED DERMATOSES

• Systemic Lupus Erythematosus (SLE) / Subacute LE / Discoid LE
• Rosacea
• Atopic dermatitis
• Seborrheic dermatitis
• Dermatomyositis
• Darier's disease
• Pemphigus
• Psoriasis (rarely)

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III. CHEMICAL/DRUG-INDUCED PHOTOSENSITIVITY

• Psoralens (psoralen + UVA = PUVA phototoxicity)
• Tetracyclines (especially doxycycline)
• NSAIDs (naproxen, piroxicam)
• Amiodarone, thiazides, fluoroquinolones, tar

• Sunscreen ingredients (benzophenones, PABA)
• Phenothiazines
• Sulfonamides
• Fragrances (musk ambrette)

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IV. METABOLIC / GENODERMATOSES

• Erythropoietic Protoporphyria (EPP) — most common porphyria with photosensitivity
• Porphyria Cutanea Tarda (PCT)
• Congenital Erythropoietic Porphyria (CEP / Günther disease)

• Xeroderma Pigmentosum (XP)
• Cockayne Syndrome
• Bloom Syndrome
• Trichothiodystrophy

• Pellagra (niacin deficiency — Casal's necklace)
• Hartnup disease

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PART 2: POLYMORPHOUS LIGHT ERUPTION (PMLE) — 10 MARKS

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Definition & Introduction

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Epidemiology

• Prevalence is inversely related to latitude: highest in Scandinavia (~22%), moderate in UK and northern USA (10–15%), low in Australia (~5%), and rare in equatorial Singapore (~1%)
• This gradient reflects UV-induced immunologic tolerance ("hardening") from year-round sun exposure in sunny climates
• Female:Male ratio = 2:1 to 3:1
• Onset typically in the second and third decades of life; all races and skin phototypes affected
• Family history positive in 10–50% of cases

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Pathogenesis

• Normal UV exposure induces local immunosuppression (regulatory T cells, IL-10) — protecting against autoimmune reactions to UV-modified skin antigens
• In PMLE patients, this UV-induced immunosuppression is defective or absent → UV-modified skin proteins act as neoantigens → CD4⁺ T-cell mediated DTH reaction is mounted
• Reduced neutrophil infiltration after UV exposure has also been documented
• Action spectrum: UVB (290–320 nm) > UVA (320–400 nm); rarely visible light
• Hardening phenomenon: Repeated UV exposure progressively restores immunosuppression → lesions diminish as summer advances

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Clinical Features

• Benign Summer Light Eruption (BSLE): mild, diffuse variant with spontaneous clearing
• Juvenile Spring Eruption (JSE): occurs on the helices of ears in children (Fig. 3.23 — swollen, red ear helix)

• V-area of chest, neck, forearms, dorsum of hands, face
• Areas protected in winter (extensor forearms, chest V-area) are preferentially affected — reflecting the "change in UV dose" more than absolute amount
• Sun-protected areas (under chin, behind ears) are spared

• Eruption appears 1–4 days after sun exposure (some report within 24 hours)
• Lesions last a few days to 1–2 weeks without scarring
• No scarring or atrophy (helps differentiate from LE and hydroa vacciniforme)
• Postinflammatory hyperpigmentation may occur in darker skin

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Histopathology

• Epidermis: Spongiosis (variable), may be normal
• Dermis: Dense, perivascular lymphocytic (CD4⁺) infiltrate in the superficial and deep dermis
• Striking papillary dermal edema — key early histological feature differentiating PMLE from LE
• No epidermal basal layer damage
• Direct Immunofluorescence (DIF): negative — important to distinguish from LE (DIF shows Ig/C3 deposits in LE)

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Investigations / Evaluation

Note: 10–20% of PMLE patients may have positive ANA and family history of lupus; photosensitive SLE may present with PMLE-like eruptions years before SLE diagnosis — these patients must be followed up.

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Differential Diagnosis

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Treatment

• Broad-spectrum sunscreens (SPF ≥ 30, UVA + UVB protection) — applied 20–30 min before sun exposure
• Protective clothing, sun avoidance (especially 10 AM–4 PM)
• Hardening/desensitization phototherapy (most effective long-term strategy):
  • Narrowband UVB (NB-UVB, 311 nm) — preferred; 15–20 sessions in spring
  • PUVA (psoralen + UVA) — for resistant cases
  • These mimic the natural hardening process

• Topical corticosteroids — moderate-to-potent; for itching and inflammation
• Oral antihistamines — for pruritus relief
• Systemic corticosteroids (short course) — for severe, extensive flares

• Hydroxychloroquine (antimalarial) — especially for frequent, severe attacks
• Azathioprine — second-line immunosuppressant
• Beta-carotene — limited evidence
• Afamelanotide (α-MSH analogue) — stimulates melanin; used in clinical trials

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Prognosis

• Spontaneous remission occurs in ~40% of patients over time (lesions become milder with advancing age)
• The hardening phenomenon means episodes are most severe in spring and become less severe as summer progresses
• Does not cause permanent scarring
• Small but important risk of later development of SLE — annual follow-up recommended

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Clinical Images

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Summary Box (for quick revision)

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• Dermatology, 5th Edition (Bolognia, Schaffer, Cerroni) — Ch. 87 (Lim HW, Rosen CF)
• Andrews' Diseases of the Skin, 13th Ed — Ch. 3 (Idiopathic Photosensitivity Disorders)
• Fitzpatrick's Dermatology, Vol. 1–2

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Classification of Annular Erythemas & EAC — 3rd Year Dermatology PG Theory

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PART 1: CLASSIFICATION OF ANNULAR ERYTHEMAS

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I. FIGURATE (GYRATE) ERYTHEMAS — "The Classic Four"

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II. INFECTIONS CAUSING ANNULAR ERYTHEMA

• Dermatophytosis (Tinea corporis) — leading scale (outer border); KOH positive
• Secondary syphilis — annular/psoriasiform plaques; serology positive
• Leprosy (Hansen disease) — hypopigmented anaesthetic annular plaques; AFB
• Lyme disease — erythema migrans (target lesion)
• Pityriasis rosea — herald patch + collarette scale

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III. AUTOIMMUNE / CONNECTIVE TISSUE DISEASE

• Subacute Cutaneous Lupus Erythematosus (SCLE) — photodistributed; anti-Ro/SSA antibody
• Annular Erythema of Sjögren's Syndrome — associated with primary Sjögren's syndrome; anti-Ro/SSA positive; most common in Japanese
• Neonatal Lupus Erythematosus — transient annular plaques; maternal anti-Ro antibody
• Rowell Syndrome — SLE + EM-like annular lesions

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IV. URTICARIAL / ALLERGIC ANNULAR ERYTHEMAS

• Urticaria — evanescent, lasts <24 h; wheals
• Erythema Multiforme — target lesions; acral > trunk
• Annular Urticaria

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V. NEUTROPHILIC / EOSINOPHILIC DERMATOSES

• Eosinophilic Annular Erythema — recurrent annular plaques; eosinophilic infiltrate; may be associated with atopy
• Wells Syndrome (Eosinophilic Cellulitis) — "flame figures" on histology

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VI. GRANULOMATOUS ANNULAR DERMATOSES

• Granuloma Annulare — skin-colored to erythematous papules in annular ring; no scale; palisading granulomas on histology
• Sarcoidosis — annular plaques; non-caseating granulomas
• Necrobiosis Lipoidica — pretibial, yellow-brown annular plaques

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VII. DERMATOLOGICAL CONDITIONS WITH ANNULAR MORPHOLOGY

• Psoriasis — annular/gyrate variant; silvery scale; Auspitz sign
• Mycosis Fungoides (CTCL) — annular/poikilodermatous patches; cerebriform nuclei on histology
• Erythema Dyschromicum Perstans (Ashy Dermatosis) — grey annular macules
• Fixed Drug Eruption — recurring at same site; post-inflammatory pigmentation

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PART 2: ERYTHEMA ANNULARE CENTRIFUGUM (EAC) — 10 MARKS

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Definition

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Epidemiology

• Can occur in any age group; peak incidence in the 3rd–5th decade (Fitzpatrick's: 5th decade; Fitzpatrick's Ch. 46: 3rd–4th decade)
• No sex predilection (equal M:F)
• A rare autosomal dominant familial form ("familial annular erythema") exists
• Occurs in infants and children rarely

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Etiology & Pathogenesis

• Dermatophytes — tinea pedis (48% in one series), tinea unguium
• Fungi — Candida, Penicillium (blue cheese ingestion)
• Viruses — EBV, VZV, poxvirus, HIV
• Bacteria — Pseudomonas, post-tonsillitis, Borrelia
• Parasites, ectoparasites (Phthirus pubis)

• Diuretics, NSAIDs, antimalarials, finasteride, amitriptyline
• Biologics: nivolumab, sorafenib, rituximab, ustekinumab, pegylated interferon-α + ribavirin

• Lymphomas, leukemias, solid organ malignancies (13% in one series)

• Pregnancy, Crohn's disease, autoimmune endocrinopathies (Hashimoto's thyroiditis), hypereosinophilic syndrome

In one third of patients, no associated cause is found (idiopathic)

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Clinical Features

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Two Variants — Superficial vs. Deep

Key examination point: Scale in EAC is "trailing" (at the inner border, just behind the advancing edge) — this contrasts with tinea corporis where scale is "leading" (at the outer advancing border)

• Lower extremities (thighs, buttocks) — most common (~48%)
• Trunk (~28%)
• Upper extremities (~16%)
• Face — typically spared

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Histopathology

• Epidermis: focal spongiosis, parakeratosis, hyperkeratosis; ± basal vacuolar changes
• Dermis: dense perivascular lymphocytic infiltrate in the superficial dermis in a characteristic "coat-sleeve" arrangement around blood vessels

• Epidermis: normal (no epidermal changes)
• Dermis: dense perivascular lymphocytic infiltrate concentrated in the upper and deep dermis — tight "coat-sleeve" arrangement

The "coat-sleeve" (sleeve-like) perivascular infiltrate is the histological hallmark of EAC — described in all major textbooks

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Investigations

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Differential Diagnosis

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Treatment

• Identify and treat the trigger (e.g., antifungals for tinea pedis → often causes resolution of EAC)
• Withdraw offending drug
• Treat underlying malignancy (paraneoplastic EAC may resolve with treatment of cancer)
• Dietary modification if food trigger identified

• Systemic corticosteroids — short courses
• Metronidazole — has been reported effective
• Erythromycin — reported benefit in some series
• Hydroxychloroquine, azathioprine, cyclosporine — anecdotal reports

Most cases eventually subside spontaneously, even without treatment, particularly if the trigger resolves.

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Prognosis

• Chronic, waxing and waning course
• Individual lesions resolve in days to months
• Total disease duration: months to years (rarely persists permanently)
• Spontaneous remission is the eventual outcome in most patients
• Recurrence possible, especially if trigger (e.g., tinea) recurs
• No scarring; postinflammatory pigmentation may persist

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Key Clinical Images

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Summary Box — EAC at a Glance

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• Fitzpatrick's Dermatology, Vol. 1–2 — Ch. 46 (Ahn CS, Huang WW — EAC & Figurate Erythemas) and Table 19.1
• Dermatology, 5th Ed. (Bolognia, Schaffer, Cerroni) — Ch. 19 (Lim HW — Figurate Erythemas)
• Andrews' Diseases of the Skin, 13th Ed. — Ch. 7 (Gyrate Erythemas)

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TUFTED ANGIOMA — 5 Marks (3rd Year Dermatology PG Theory)

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Definition

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Epidemiology

• Rare; no sex predilection
• ~25% are congenital; ~50% appear within the first year of life; over 50% present before age 5 years
• Adult onset described but uncommon
• Sporadic in the vast majority; rare familial cases reported
• Current consensus: TA represents a superficial, milder form of Kaposiform Hemangioendothelioma (KHE) on a shared histopathologic and molecular spectrum

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Pathogenesis

• Etiology uncertain; based on immunostaining profile, a lymphatic endothelial origin is postulated
• TA and KHE share histologic and molecular overlap — considered part of a continuous spectrum
• Peripheral lesion growth reflects localized production of proinflammatory cytokines and vasoactive peptides
• Unlike infantile hemangioma, no GLUT-1 positivity; no known gender or gestational age correlates
• Platelet trapping within the tumor lobules leads to Kasabach-Merritt phenomenon in some cases

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Clinical Features

• Begins as a subtle, poorly defined dull-red/violaceous macular stain that slowly thickens
• Evolves into a poorly defined, mottled red-dusky plaque (2–5 cm or larger) with superimposed angiomatous papules
• Can present as an exophytic, firm, rubbery violaceous nodule
• Associated features: overlying hypertrichosis (lanugo-like hair), hyperhidrosis, tenderness/pain (especially during KMP exacerbations)

• Most common: neck, upper trunk, shoulders
• Also: extremities, lower trunk; rarely face

• Slow centrifugal growth over months to years → eventual stabilization
• Rarely: complete spontaneous regression (more likely in congenital/early infantile lesions; 95% of regressing TAs do so within 2 years)
• Usually solitary; multifocal cases reported

• Occurs more in congenital TAs and KHE
• Characterized by profound thrombocytopenia, microangiopathic hemolytic anemia, and consumptive coagulopathy due to platelet trapping within the tumor
• Life-threatening if untreated; elevated D-dimers, low fibrinogen

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Histopathology — "Cannonball Pattern" (Hallmark)

• Multiple discrete lobules of tightly packed capillaries randomly scattered within the dermis and subcutis
• Lobules have a characteristic "cannonball" distribution — rounded clusters dispersed haphazardly through the dermis
• Capillary lumina are pinpoint-sized, occasionally containing fibrin microthrombi
• Lobules bulge into peripherally placed thin-walled lymphatic-like spaces (crescent-shaped spaces around tufts)
• Mitotic figures are rare
• Endothelial cells: may be focally spindled but less prominent than in KHE
• Dermal collagen between lobules may be normal or fibrotic

GLUT-1 negativity is the key differentiating feature from Infantile Hemangioma

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Differential Diagnosis

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Clinical Images

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Management

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Summary Box

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• Fitzpatrick's Dermatology, Vol. 1–2 — Ch. 118 (Tufted Angioma)
• Dermatology, 5th Ed. (Bolognia, Schaffer, Cerroni) — Ch. 114 (Lim HW/Rosen — Vascular Tumors)
• Andrews' Diseases of the Skin, 13th Ed. — Ch. 28