A skin rash may represent a systemic disorder of various types such as nutritional deficiency, infection, rheumatological disorder or malignancy or it could be due to skin diseases such as infection or atopy. The type of skin rash, localised or generalised and with or without itching, and certain diagnostic clues can help narrow down diagnostic probabilities.

Appearance of a skin rash

Skin rash may present with a change in colour (red, pigmented) or appearance in the form of a macule (flat), papule (raised), vesicle (fluid-filled), bulla (large), pustule (pus-filled), crust, scaly, peeling or roughness of skin as well as a dry or wet lesion.

Skin rash may be blanching, transient fading on pressure that indicates inflammatory rash. The morphological characteristics are shared by different diseases and hence do not help in isolation for specific aetiological diagnoses.

Diagnostic clues to observe

1. Sick or not sick- Sickness may be evident in the form of tiredness, inactivity, lethargy, confused state, irrelevant talking or irritability. It suggests a systemic disorder. The degree of sickness may guide to consider aggressive management.
2. Itching- It may be obvious as scratch marks on the skin would indicate itchiness. While atopic conditions or local skin infections such as scabies and fungal infections lead to itching, even some of the viral infections such as coxsackie or echovirus, deep-seated bacterial infections and lymphoma may also result in itching. Besides, cholestatic jaundice also causes severe itching due to the retention of bile acids.
3. Erythema- Pink or red flush on the skin (like a slapped face) may be a manifestation of a viral infection such as parvovirus (also known as erythema infectiosum or fifth disease).
4. Maculopapular rash- It is seen in many viral infections or may be due to nutritional deficiency or drug-induced and per se has no diagnostic significance. However, a skin rash may have a predilection to either the central or peripheral part of the body that may suggest a particular type of infection.
5. Vesicular rash- It is typically seen in varicella or a few other viral infections. It may also be due to a severe toxic reaction to an infection or drugs (Steven-Johnson syndrome).
6. Pustular rash- It is a result of local skin infection as in the case of impetigo or a secondary bacterial infection following local skin injury.
7. Haemorrhagic rash- It may present as purpura or ecchymosis and result from a bleeding disorder or vasculitis.
8. Gangrenous rash- It presents as blackish dying tissue as a result of a peripheral vascular obstruction in the fingers, toes or ear lobule. It indicates a severe complication of an infection such as Rickettsia.
9. Hyperpigmented patch- It may be present as a localised lesion (melanoma) or may be present since birth and disappear over a year (Mongolian spots). Scattered hyperpigmentation may indicate adrenal disorder or vitamin B12 deficiency (knuckle pigmentation).
10. Hypopigmented patch- It presents as a whitish patch, often a result of local skin damage due to any kind of inflammation. Leprosy may present with such a patch (loss of sensation is characteristic). Pinkish white patches scattered over the body are due to leukoderma.
11. Peeling of skin- It indicates dying skin that is being shed for new skin to appear that may take a few days to weeks. It may be restricted to small areas as in case of local irritation or maybe widespread due to systemic disorders such as scarlet fever-toxic reaction to bacterial infection or an immune disorder such as Kawasaki disease.

How does general observation help?

The following examples would reiterate the importance of general observation of skin:

Case 1

A child presented with a macular skin rash. He was not sick looking, had evidence of bilateral cervical swelling, mostly enlarged lymph nodes, and inflamed throat with greying membrane on tonsils.

Diagnosis: This is typical of EB viral infection.

Case 2

A child presented with a macular skin rash, redness of eyes and mouth, single large swelling on the neck, mostly enlarged lymph node, and peeling of the skin on fingers. He was irritable looked sick.

Diagnosis: This suggests Kawasaki disease.

Case 3

A child presented with a skin rash that was scattered all over with large size vesicles filled with clear fluid. He looked very sick and had mouth ulcers.

Diagnosis: It may be Steven-Johnson syndrome, a drug reaction, or haemorrhagic varicella.

Case 4

A child presented with scattered skin rash and pinpoint red spots, considered to be purpura on observation. No other bleeding manifestations were seen but he looked very sick.

Diagnosis: It could be either vasculitis, a result of severe bacterial infection such as meningococcemia or maybe a primary haematological disorder such as leukaemia.

Case 5

A child presented with severe itching lesions over the body. It looked like inflamed areas more at flexural surfaces, most of them being dry and rough, but also had the occasional ones with wet surfaces.

Diagnosis: It is typically atopic dermatitis.

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.