Photosensitivity

Am J Dermatopathol. 2006 Dec;28(6):482-485. Abstract quote

Dermatoses associated with cutaneous photosensitivity are a group of photodistributed skin eruptions caused or exacerbated by light. Multiple clinical variants of photosensitive dermatoses have been characterized including polymorphous light eruption, chronic actinic dermatitis, solar urticaria, phototoxic and photoallergic dermatitis, reticular erythematous mucinosis, acute cutaneous lupus erythematosus, and dermatomyositis. As there may be significant overlap among the clinical presentation of these conditions, the specific diagnosis of individual photodermatosis relies heavily on characteristic histopathologic features.

We present here 5 cases of photodistributed eruptions with virtual absence of histologic epidermal changes and dermal inflammation, yet all were described clinically as being "inflammatory" and erythematous. All cases of this "pauci-inflammatory photodermatitis" presented with photodistributed bright red macular erythema or slightly indurated plaques that developed over a period of weeks to months and clinically resembled photoallergic or phototoxic drug reactions or polymorphous light eruption.

Microscopically, however, only very sparse dermal lymphocytic infiltrate was noted with no or minimal epidermal changes.

To our knowledge, the observation of clinically evident photodistributed dermatoses that demonstrate such minimal histopathologic findings has not been reported. Clinicians and histologists should be aware of the disparity that may be encountered in this setting, as the clinical features are usually far more impressive than those seen histologically.

Epidemiology
Disease Associations
Gross Appearance and Clinical Variants
Differential Diagnosis
Prognosis
Treatment
Commonly Used Terms
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GROSS APPEARANCE/CLINICAL VARIANTS	CHARACTERIZATION
General
VARIANTS
INFANCY WITHOUT TELANGIECTASIA	Xeroderma pigmentosum Erythropoietic porphyria Erythropoietic protoporphyria Hydroa vacciniforme
INFANCY WITH TELANGIECTASIA	Bloom's syndrome Cockayne's syndrome Rothmund-Thomson syndrome
ADULTS-HERITABLE/METABOLIC DISEASES	Xeroderma pigmentosum Erythropoietic porphyria Erythropoietic protoporphyria Porphyria cutanea tarda Variegate porphyria
IN COLLAGEN VASCULAR DISEASES	Systemic lupus erythematosus Subacute cutaneous lupus erythematosus Dermatomyositis
DRUG INDUCED
PHOTOTOXIC	Tetracyclines Psoralens
Diltiazem-Associated Photodistributed Hyperpigmentation A Review of 4 Cases	Arch Dermatol. 2001;137:179-182
PHOTOALLERGIC	Thiazides Sulfonylureas
PHOTOCONTACT
MISCELLANEOUS	Actinic reticuloid

HISTOPATHOLOGY	CHARACTERIZATION
VARIANTS
Photodermatitis with Minimal Inflammatory Infiltrate: Clinical Inflammatory Conditions with Discordant Histologic Findings. Su W, Hall BJ 4th, Cockerell CJ. *From the Department of Pathology, Upstate Medical Center, Syracuse, New York; and the daggerDepartment of Dermatology, University of Texas Southwestern Medical Center, Dallas, Texas.**	Am J Dermatopathol. 2006 Dec;28(6):482-485. Abstract quote Dermatoses associated with cutaneous photosensitivity are a group of photodistributed skin eruptions caused or exacerbated by light. Multiple clinical variants of photosensitive dermatoses have been characterized including polymorphous light eruption, chronic actinic dermatitis, solar urticaria, phototoxic and photoallergic dermatitis, reticular erythematous mucinosis, acute cutaneous lupus erythematosus, and dermatomyositis. As there may be significant overlap among the clinical presentation of these conditions, the specific diagnosis of individual photodermatosis relies heavily on characteristic histopathologic features. We present here 5 cases of photodistributed eruptions with virtual absence of histologic epidermal changes and dermal inflammation, yet all were described clinically as being "inflammatory" and erythematous. All cases of this "pauci-inflammatory photodermatitis" presented with photodistributed bright red macular erythema or slightly indurated plaques that developed over a period of weeks to months and clinically resembled photoallergic or phototoxic drug reactions or polymorphous light eruption. Microscopically, however, only very sparse dermal lymphocytic infiltrate was noted with no or minimal epidermal changes. To our knowledge, the observation of clinically evident photodistributed dermatoses that demonstrate such minimal histopathologic findings has not been reported. Clinicians and histologists should be aware of the disparity that may be encountered in this setting, as the clinical features are usually far more impressive than those seen histologically.

CHARACTERISTIC	PHOTOTOXIC	PHOTALLERGIC
Incidence	Usually relatively high	Usually relatively low
Clinical	Resemble sunburn	Varied
Possibility of reaction on first exposure	Yes	No
Incubation period after first exposure	No	Yes
Development of persistent light reaction	No	Yes
Possibility of flares at distant previously involved sites	No	No
Cross reactions to structurally related agents	No	Frequent
Broadening of cross reactions following repeated photopatch testing	No	Possible
Concentration of drug necessary for reaction	High	Low
Chemical alteration of photosensitizer	Sometimes	Yes
Covelent binding with carrier protein	No	Yes
Langerhans cell required	No	Yes
Cellular passive transfer	No	Yes
Lymphocyte stimulation test	No	Yes
Macrophage migration inhibition test	No	Yes