Table 2.

Similarities and differences in the clinical appearance of autoimmune or immune-mediated dermatological diseases and bed bug bites

Diagnosis		Similarities	Differences
Autoimmune/immune-mediated diseases:
	Allergic contact dermatitis [58]	Papules, vesicles or bullae, with erythematous base and distinct border. Severe itching	Vesicles tend to coalesce. Patients may report the causative agent
	Bullous pemphigoid [5]	Tense bullae with erythematous base, severe itching. Limbs and the trunk region are mostly affected	Elderly people are affected. Symmetrical. Affects flexural areas of the limbs and also mucosa
	Dermatitis herpetiformis [59]	Papules, vesicles on the extensor surfaces of the thighs, elbows, buttocks. Extensive itching	Symmetrical appearance, long-term history. Associated with intestinal symptoms in 20%
	Erythema multiforme [60]	Erythematous-blanche “targetoid” lesions on elbows, palms and knees. Blisters can occur	Symmetrical. Pain and mucosal involvement can occur. HSV infection or drug intake often precede symptoms
	Linear IgA dermatosis [61]	Tense vesicles and bullae, erythematous base	Annular distribution. Mucous membrane involvement can occur
	Lymphomatoid papulosis [62]	Erythematous/red-brown papulonodules. Central ulcerations can occur. Limbs and trunk region	Single or few lesions. Chronic recurrent. Often leaves residual scarring
	Papulovesicular polymorphous light eruption [63]	Erythematous blisters, papules. Itching can occur	Monomorphic lesions in a given patient. Eruptions after sunlight-exposure, on sun-exposed areas
	Phytophotodermatitis [64]	Blisters, plaques in a linear distribution affecting the distal part of extremities	After outdoor activity. Continuous lines, not solitary papules in linear pattern
	Pityriasis lichenoides chronica [65]	Erythematous papules, nodules. Limbs and trunks are commonly affected sites	Prominent scaling, shiny surface. Lesions are at different stages of development. Long-term history
	Pityriasis lichenoides et varioliformis acuta [66]	Erythematous papules, vesicles. May be pruritic. Central haemorrhage mimics the punctum. The trunk and limbs are mostly affected	Scaling, lesions at different stages. Affects flexural sites of extremities. Linear pattern is missing
	Prurigo nodularis [67]	Excoriated erythematous papules, nodules, severe itching. Affects extensor surface of limbs	Symmetrical. The central back is spared. Long-term history, slow development
	Pruritic urticarial papules and plaques of pregnancy [68]	Pruritic, erythematous wheals, papules, plaques, seropapules. Linear arrangement	Linearity follows striae with periumbilical sparing. Proximal region of the limbs is affected. Onset in the third trimester of pregnancy
	Sweet-syndrome [69]	Erythematous to purple, tender papules, plaques, blisters. Limbs, neck and upper back region	Fever, neutrophilia is present. May involve mucosa and other organs. Onset after infection, drug intake or chronic illness
	Toxicoderma [70]	Wheals, maculopapules, blisters. Itching can occur	Drug intake in history, time lapse from drug intake is 1–21 days. Lesions tend to coalesce, head-to-toe change in distribution
	Urticaria [71]	Multiple hives, intensely itching	Vary in size and shape. Changing location in maximum 48 h. Appear anywhere on the body
	Urticaria vasculitis [71]	Erythematous hives, central palpable purpura. Lesions last over 48 h	Vary in size and shape. Residual central hyperpigmentation. Pattern is not linear