Covid-19 (an acronym for CoronaVirus Disease) is an infectious disease caused by a coronavirus called SARS-CoV-2 (previously referred to as 2019-nCoV). Although the term “SARS” (Severe Acute Respiratory Syndrome) refers to respiratory manifestations, this infection can cause severe multi-organ manifestations and is by no means limited exclusively to pulmonary involvement. As the skin is the largest organ of our body, it is not surprising that multiple and varied cutaneous manifestations have been described whose presence can help us to suspect this potentially serious infection.
As is well known, there are two vectors that condition the severity and eventual mortality of this process: the action of the virus itself and an occasional “exaggerated” inflammatory response that conditions our own immune system. Although the cutaneous manifestations described are very varied and inconsistent, five more or less recognizable patterns have been described. Quite often, these manifestations can “simulate” other cutaneous processes totally unrelated to this situation and with which the differential diagnosis should be made.
1. Maculo-papular rash
This is probably the most frequently observed pattern in patients with Covid-19. It consists of multiple lesions widely distributed over the skin, symmetrically or anarchically located. The term “maculo-papular” refers to the lesions being “macules” (non-palpable reddish spots) or “papules” (also erythematous lesions more or less raised or palpable). This rash may be indistinguishable from other viral exanthem and may simulate other processes such as measles or pityriasis rosea. Although it usually predominates on the trunk, lesions have been described in other locations. It is not usually associated with mucosal manifestations (“enanthema”).
The rash may be accompanied by pruritus (itching) although this is usually mild (or absent). The lesions are very variable (scaly or smooth, simply erythematous or purpuric, with or without itching) and, obviously, non-specific. Among many other possibilities they can be mistaken for skin reactions to some of the drugs used (“toxicoderma”). This pattern usually begins within a few days of respiratory or systemic manifestations and is more frequent in severe cases.
2. Urticarial rash
It manifests with wheals (“hives”) reminiscent of urticaria. Although they have been described on the face and distal areas of the extremities, they usually predominate on the trunk and the roots of the arms and thighs. In this case itching is very frequent.
Although it is usually seen in patients who already have respiratory or other organ symptoms, sometimes it may precede it. Urticaria is very common and its causes are numerous, so an asymptomatic patient with urticaria should not be overly alarmed since, although Covid infection should be ruled out, it is very likely that the tests are negative and it is simply “normal” urticaria. Even in patients already diagnosed with Covid it may be difficult to distinguish this manifestation from urticaria. In both “conventional” urticaria and in this manifestation of SARS-CoV-2 infection, the lesions may be annular (ring-shaped wheals).
3. Varicelliform pattern
This is a rash reminiscent of chickenpox and, like chickenpox, the lesions are usually vesicular (small fluid blisters) or crusted (vesicles that are already desiccated or excoriated). Although, like chickenpox, fever is almost constant, there are two details that may help in the differential diagnosis.
Unlike chickenpox, the lesions produce little or no itching and all of them are seen in the same evolutionary phase (“monomorphic” picture that differs from the “starry sky image” of chickenpox, in which new lesions are seen together with other more evolved or crusted lesions). Another difference is that there are usually no lesions on the face or mouth. Although it has also been observed more frequently in patients already diagnosed with Covid, there are more than 10% of cases in which this rash may precede any other manifestation.
4. Perniosis type lesions (“chilblains”)
Within the so-called “acral manifestations” (fingers and toes above all) it has long been observed that some patients present lesions quite similar to perniosis or chilblains. They represent about 20% of the cutaneous manifestations of Covid-19. Perniosis, nowadays, is not very frequent in environments where it is not as cold as it was many years ago. Therefore, what was more or less common until the first half of the last century is now rare in urban areas. This fact makes the suspicion of SARS-CoV-2 infection higher in people who develop this type of pathology.
Apart from the toes, areas on the soles of the feet may be affected and lesions may range from simple localized reddening to the formation of purpuric lesions (purplish or dark red lesions) and even blisters. Unlike true chilblains, about one third of patients do not experience itching or pain. This pattern is more frequent in asymptomatic young people or those with less severe manifestations of the disease.
5. Livedoid” pattern
The so-called “livedo reticularis” or “livedo racemosa” is a cutaneous sign in which color changes appear, somewhat bluish in hue, in a pattern reminiscent of a net. It is usually predominant in the lower extremities and, although it can be seen in isolation, its presence forces us to rule out multiple systemic diseases. This pattern, which is probably the least frequent, has been seen more in very severe and often intubated patients. Therefore, it is not helpful for an early suspicion of infection. These color changes can lead to areas of ischemia (lack of blood supply) and progress to hemorrhagic lesions, skin necrosis or gangrene.
Thus, the first and last mentioned patterns can rarely alert the physician or the patient for diagnostic testing since they usually occur in patients already diagnosed and often already admitted.