Final answer:
The patient's symptoms of severe pruritis and S-shaped tracks on the skin with scabs are indicative of scabies, which is caused by the burrowing mite Sarcoptes scabiei. This diagnosis is distinct from psoriasis, contact dermatitis, or atopic dermatitis, which do not produce burrow tracks.
Step-by-step explanation:
The most likely diagnosis for a patient with severe pruritis of the upper extremities and S-shaped tracks on the skin surface with multiple scabs is scabies. Scabies is a skin infestation caused by a mite known as Sarcoptes scabiei. These mites burrow into the skin, causing an allergic reaction and intense itching, which leads to the characteristic S-shaped tracks cited in the question. The tracks are actually the burrows created by the mites and the scabs are from scratching due to severe itchiness. This symptomatology is distinct and does not typically overlap with the common presentations of psoriasis, contact dermatitis, or atopic dermatitis (eczema), which although can cause itching, they do not create the tunnel-like tracks found in scabies.
While psoriasis is associated with itchy or sore patches of thick, red skin with silvery scales, it does not cause burrows in the skin. Similarly, contact dermatitis results from skin contact with an allergen or irritant causing localized redness, swelling and itching, but not the S-shaped burrows. Finally, atopic dermatitis, also known as eczema, presents as dry, itchy patches that resemble rashes and is caused by an allergic reaction, but again, lacks the burrowing mite as its source.
Scabies is the likeliest diagnosis due to the symptom of S-shaped tracks on the skin, which represents mite burrows and is the key distinguishing factor compared to symptoms of similar itchy skin conditions like psoriasis, contact dermatitis, or atopic dermatitis (eczema).