Tinea of the scalp may be confused with any scalp disorder that causes patchy alopecia, inflammation, or scale. The presence of hairs broken off a short distance above or right at the scalp surface should cause immediate suspicion. Occasionally TCa does not produce hair breakage.
The noninfectious dermatidities seborrhea and psoriasis can both cause inflammation and scaling of the scalp, but do not cause patchy hair shedding. Both are more diffuse than TCa. When any inflammatory scalp condition does not respond promptly to treatment, a KOH exam and fungal culture of epilated hairs are indicated.
Alopecia areata causes patchy hair loss and may show erythema of the scalp. Scale is absent, however, and the presence of exclamation-point and dystrophic anagen hairs should differentiate it. In older patients with alopecia areata, gray hairs continue to grow within the patches of alopecia.
Trichotillomania, which is frequent in children, presents with patchy areas of hairs that are broken off at differing lengths above the scalp. Inflammation and scale are usually absent. When inflammatory change is present, there is usually associated lichenifica-tion. These secondary changes are more common in adult cases.
An active impetigo of the scalp, on rare occasions, can produce enough inflammation to cause hair loss and may simulate a kerion. Hairs can be readily epilated but come out by the root rather than by breakage. Whenever there is a question, hair KOH exam and fungal culture are indicated.
Chronic staphylococcal folliculitis and TB may be very difficult to distinguish because TB usually has a component of secondary infection that will respond to broad-spectrum antibiotics. One should always be suspicious when there is rapid relapse of a facial folliculitis after appropriate antimicrobial therapy.
Gram-negative folliculitis can also be confused with TB; however, the pustules are usually painful and not pruritic. They are dusky red and have a straw-colored surface pustule. Bacterial culture will usually distinguish between them.
Because this form of tinea occurs on a sun-exposed area and subjective symptoms exacerbate with sun exposure, it is not infrequently confused with discoid lupus and other light eruptions that affect the face. The similarity can be striking. Look carefully for an active advancing margin and for follicular pustules. A simple KOH exam of the scale can prevent an important misdiagnosis.
Patches of nummular eczema, early lesions of psoriasis, patches of impetigo, pityriasis alba in its early inflammatory phase, and the herald patch of pityriasis rosea can all be confused with TC. When other diagnostic features of these conditions are absent, a simple KOH exam should distinguish them.
Erythrasma of the groin is less inflammatory and less symptomatic than TCr. In addition, it lacks the active border and gives a coral-red fluorescence when exposed to a Wood's lamp.
Intertriginous monilia is more inflammatory, and the usual complaint is soreness and itching. The area has a deep-red burnished or moist appearance. The margin is sharp but is not raised as in TCr and there are small satellite lesions and pustules beyond the edges.
Bacterial intertrigo is usually more inflammatory and associated with an offensive odor. This is almost always seen in obese persons and shows a symmetric sharp but not raised margin, which corresponds to the areas of skin opposition.
Bacterial intertrigo, candidiasis, erythrasma, or Gram-negative toe web infections may be difficult to distinguish from intertriginous tinea of the feet. Wood's lamp exam will show coral-red with erythrasma and green-blue with intertriginous pseudomonas. Otherwise a KOH preparation or fungal culture are indicated.
Eczema, although common on the feet, rarely affects the toe webs. Dry scaling fungal infections of the palms and soles are difficult to confuse with other conditions. A simple KOH exam should establish the diagnosis because the surface is usually teeming with hyphae.
Dyshidrosis or contact dermatitis may be easily confused with vesicular fungal infections of the palms and soles. A KOH exam of an inverted blister roof is almost always positive if it is a dermatophytosis. Remember, active TP can cause a sympathetic id reaction (see Photo 19) on the hands, and those vesicles are KOH negative. Both areas should be tested.
Psoriasis, lichen planus, monilia of the nails, and other nondermatophyte fungal and yeast organisms that invade nail tissue must be distinguished from onychomycosis of the nails.
Psoriasis may be clinically very similar. Fine linear pitting of psoriasis is not a feature of TU. Another helpful sign is the oil-spot change on the nail bed seen in psoriasis.
Lichen planus usually attacks the proximal nail fold, causing scarring and nail dystrophy. Lysis of the plate occurs but is usually "clean" without the debris and buildup seen with TU.
Monilia can cause distal lysis and is usually tender with minimal scale distortion or debris. When the proximal nail fold is involved, there are pain and swelling not seen with TU. To confirm a dermatophyte infection versus other nail pathogens, obtain nail cultures.
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