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Rash in Children: Differential Diagnoses

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Overview

Rash is a common symptom seen in children and its differential diagnoses range from self-limiting conditions to life-threatening illnesses such as meningococcal meningitis.

Its differential diagnoses can be categorised on the morphology of the rash and associated features:

  • Vesiculobullous rashes
  • Pustular rashes
  • Macular and/or papular rashes
  • Red and scaly rashes
  • Red, non-scaly, and non-purpuric rashes
  • Red and purpuric rashes

Differential Diagnoses: Vesiculobullous

Varicella zoster (chickenpox)

  • Febrile prodrome
  • Itchy, vesicular rash, starting on the head and trunk before spreading
  • Crusting occurs within 5 days of the rash

Herpes simplex virus

  • Prodrome of a burning sensation followed by the emergence of erythematous vesicles
  • May cause eczema herpeticum in children, which is characterised by:
    • A rapidly-progressing painful rash
    • Grouped vesicles and punched-out circular ulcerated lesions are seen
    • Fever, lymphadenopathy, and malaise may be seen
  • If eczema herpeticum is suspected, arrange immediate hospital admission

Impetigo

  • Very contagious and there is usually a history of exposure to someone with infection
  • Golden, crusted lesions form, usually around the mouth
  • Due to Staphylococcus aureus

Staphylococcal scalded skin syndrome (SSSS)

  • Prodrome of fever, malaise, and skin tenderness followed by emergence of rash
  • The rash appears blistered with scalded skin, skin exfoliation, and Nikolsky’s sign is present

Toxic epidermal necrolysis (TEN)

  • There may be a history of the use of a drug that can cause TEN (e.g. phenytoin, penicillins, carbamazepine, NSAIDs, and sulfonamides)
  • Systemically unwell with fever, tachycardia etc.
  • Red, painful macular/papular rash with the formation of bullae that coalesce
  • The rash includes the mucosal surfaces
  • The skin may slough and Nikolsky’s sign is positive
  • TEN is thought to be the more severe end of Stevens-Johnson syndrome

Stevens-Johnson syndrome

  • There may be a history of the use of a drug that can cause TEN (e.g. phenytoin, penicillins, carbamazepine, NSAIDs, and sulfonamides)
  • Initially a maculopapular rash with target lesions (pathognomonic) that may develop into vesicles and bullae which can rupture
  • The rash includes the mucosal surfaces
  • Nikolsky’s sign is positive

Erythema multiforme

  • There may be a history of the use of a drug that can cause TEN (e.g. phenytoin, penicillins, carbamazepine, NSAIDs, and sulfonamides)
  • There may be a history of an infection with herpes simplex, Epstein-Barr virus, or Mycoplasma pneumoniae
  • Target lesions are present on the extremities before spreading to the torso
  • Mucosal involvement may be present but tends to be mild and only present in one mucosal surface

Pompholyx

  • Usually precipitated by humidity and high temperatures
  • Itchy vesicles form on the palms and soles. They sometimes may feel like they are ‘burning’

Differential Diagnoses: Pustular

Acne vulgaris

  • Papules, pustules, and open/closed comedones on the face, back, shoulders, and chest
  • Most common in adolescents

Folliculitis

  • There may be a history of skin trauma (e.g. shaving, friction etc.) or excessive sweating, humidity, or may be due to infection (most commonly Staphylococcus aureus)
  • Small erythematous pustules and papules form at the base of hairs
  • They may be itchy

Differential Diagnoses: Macular and/or papular

Molluscum contagiosum

  • Skin-coloured papules with a central dimple in clusters over the body
  • As it is contagious, there may be exposure to another affected person or sharing of towels etc.
  • Lesions are not usually seen on the palms and soles

Hand, foot, and mouth disease

  • Due to coxsackie A16 or enterovirus 71
  • Febrile prodrome followed by oral ulcers within 1-2 days
  • Macules and papules appear on the hands and feet soon after the oral ulcers

Keratosis pilaris

  • Small red papules at the base of hairs that usually have no other symptoms, there may be associated pruritus

Milia

  • Most commonly seen in neonates
  • Small, benign, keratin-filled cysts that form white/yellowish bumps on the face, neck, and trunk
  • The neonate is otherwise well

Urticaria

  • ‘Hives’, erythematous, raised itchy, skin, the centre of the lesion may be more pale
  • Associated with nettles, some drugs (e.g. aspirin, penicillin, and NSAIDs), and allergy
  • May be associated with anaphylaxis 

Scabies

  • There may be exposure to a person with infection
  • Intense itchiness that may be worse at night, excoriations, linear burrows on the sides of fingers, wrist flexor surface, and between fingers

Rheumatic fever

  • There is usually a history of a recent Streptococcus pyogenes infection (around 2-4 weeks preceding the rash)
  • Fever, arthralgia, sore throat, chest pain, Sydenham’s chorea (a late sign)
  • Erythema marginatum – macules and papules that spread outwards in a circular shape with raised, red edges (margins), found on the trunk, upper arms and legs, but nearly never the face, arms or soles

Differential Diagnoses: Red, Scaly

Atopic eczema

  • Itching is a key feature – less likely to be atopic eczema if there is no itch
  • There may be a personal/family history of atopy
  • Red, dry, scaly skin on the face or extensor surfaces
  • In older children/adults, the flexors of the limbs and skin creases tend to be affected

Irritant contact dermatitis (including nappy rash)

  • Burning, stinging sensation
  • Red, dry, scaly skin confined to the areas exposed to the irritating agent (e.g. the groin area in a nappy rash, due to exposure to urine and faeces)

Allergic contact dermatitis

  • Eczematous rashes (red, scaly, dry skin) tend to be localised to a specific area after exposure to a certain allergen
  • Signs and symptoms tend to occur 24-72 hours after exposure due to allergic contact dermatitis being a delayed-type hypersensitivity reaction

Seborrhoeic dermatitis

  • Well-demarcated erythematous lesions with greasy scale
  • Often found on the cheeks, scalp (‘cradle cap)’, extremities, and trunk
  • Non-pruritic

Psoriasis

  • The rash appears as well-circumscribed plaques with silvery scales
  • Nail pitting may be seen
  • The rash tends to be found on the extensor surfaces of the knees and elbows 

Tinea corporis (ringworm)

  • There may be contact with another affected person or sharing of towels etc.
  • Annular (ring-shaped), scaly rash with slightly elevated red, sharp edges with pale centres
  • Usually seen on the trunk, extremities, or face

Tinea capitis (scalp ringworm)

  • There may be contact with another affected person or sharing of towels etc.
  • Patchy hair loss with scaling
  • If untreated, a boggy mass known as a kerion may form

Pityriasis rosea

  • There is often a herald patch followed by erythematous, scaly, oval patches over the trunk similar in appearance to a ‘fir tree’ and tend to be less widely distributed
  • There may be a history of a recent viral infection

Pityriasis versicolor

  • Tends to cause flatter, less widely-distributed lesions that may be hypopigmented, pink, or brown
  • Often noticed after a holiday when the person has been exposed to the sun

Differential Diagnoses: Red, Non-Scaly, Non-Purpuric

Cellulitis

  • There is usually a history of skin damage (e.g. trauma, wounds, or other conditions damaging the skin barrier) 
  • Erythema, pain, and swelling of an affected area
  • Edges are usually well-defined, but some cases can have diffuse erythema
  • There may be features of systemic upset including fever, malaise etc. 

Scarlet fever

  • Due to Group A Streptococcus (Streptococcus pyogenes)
  • Febrile prodrome for 12-48 hours with a sore throat
  • Blanching rash on the trunk spreading to the rest of the body – red, pinpoint (punctuate), generalised, and rough (sandpaper-like)
  • Rash may be accentuated in skin folds
  • Strawberry tongue
  • Circumoral pallor
  • Notifiable disease – notify Public Health England

Measles

  • Febrile prodrome and conjunctivitis
  • Koplik’s spots
  • Rash on ears and face before spreading to the rest of the body
  • Notifiable disease – notify Public Health England

Rubella

  • Febrile prodrome may be present
  • Pink/light-red maculopapular rash starting on the face before spreading to the body
  • Suboccipital/post-auricular lymphadenopathy may be present
  • Notifiable disease – notify Public Health England

Parvovirus B19

  • Biphasic illness with febrile prodrome 1-2 days before the rash
  • Rash develops as the child gets better – erythematous and macular on one or both cheeks resembling ‘slapped cheeks’
  • Rash may spread to the torso and extremities and becomes reticular

Roseola infantum

  • Febrile prodrome 3-5 days before the rash
  • Rash – maculopapular rash on the trunk before spreading to the face, neck, and arms
  • The rash itself does not usually cause discomfort and is not itchy
  • Febrile convulsions occur in up to 15% of patients

Kawasaki disease

  • Usually seen in children <5 years old with prolonged fever ≥5 days
  • Redness, swelling, and maculopapular rash on the palms and soles that desquamate (the skin peels) 
  • Bilateral conjunctivitis, bright red and cracked lips, ‘strawberry tongue’, cervical lymphadenopathy

Differential Diagnoses: Red, Purpuric

Meningococcal meningitis

  • Initially, the rash may be maculopapular and blanch, but as time goes on, petechiae or purpura form that do not blanch (usually on the extremities)
  • Associated features may be non-specific and do not always include the classic neck stiffness and photophobia seen. They may include fever, headaches, nausea, vomiting, anorexia, irritability, listlessness, fatigue, pallor, mottled skin, apnoea, and respiratory distress

IgA vasculitis (Henoch-Schönlein purpura)

  • There may be a history of a recent upper respiratory tract infection
  • Purpuric rash over the extensor surfaces of the arms and legs and buttocks
  • Polyarthritis
  • Abdominal pain
  • IgA nephropathy (recurrent episodes of haematuria and slight proteinuria)
  • Hypertension may be present

Immune thrombocytopenia (ITP)

  • There may be a history of a recent viral infection or the rash may appear post-immunisation
  • Petechiae and purpura in an otherwise well child
  • Remember to keep Child Maltreatment in mind
  • Full blood count shows isolated thrombocytopenia, everything else is normal

Leukaemia

  • Easy bruising and bleeding – petechiae and purpura, bleeding gums
  • Hepatosplenomegaly
  • Joint and bone pain
  • Constitutional symptoms such as fever, night sweats, unexplained weight loss, anorexia, malaise

Child maltreatment

  • See Child Maltreatment
  • Inconsistent/inappropriate explanations for the child’s presentation (e.g. fractures in non-mobile infants)
  • Associated injuries and bruising, delay in presentation, frequent attendances to hospital, recurrent trauma
  • Features of neglect (e.g. unhygienic), behaviours inconsistent with the child’s age/development (e.g. fearful and withdraw, overly friendly, overly comforting in distress, inappropriate sexual behaviour)
  • Skin lesions may include, bruises, lacerations, scalds, scratches
    • Bruising on non-bony parts of the body including the abdomen is unusual
    • Lacerations over areas usually covered with closes, including the abdomen, are unusual
    • Skin lesions such as bruising in non-mobile children are unusual

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