A diverse collection of diseases in the differential
The differential diagnosis for a rash such as the one our patient had includes tinea manuum, contact dermatitis, syphilis, and palmoplantar keratoderma (PPK).
Tinea manuum is caused by a dermatophyte infection that involves the hands. Its characteristic features are dry hyperkeratotic plaques with thin or coarse scaling on the palms. It often affects the palmar surface and, occasionally, the dorsal aspect of the hands. In most patients, it is associated with tinea pedis, a condition called “two feet-one hand syndrome.” The most common causative organism is Trichophyton rubrum.5
Diagnosis is confirmed by the presence of fungal hyphae in skin scrapings dissolved in 10% potassium hydroxide (KOH) and examined by light microscopy. It can be treated with a topical antifungal agent. However, in the case of hyperkeratotic or intractable disease, an oral antifungal medication may be needed.
Contact dermatitis is a common inflammatory dermatosis involving the hands, and many cases can be linked to the person’s job. It is often seen in individuals who need to wash their hands frequently (eg, health care workers) and those who are exposed to detergents (eg, restaurant workers).6
Clinical manifestation varies depending on the stage of eczematous progression. In the acute stage, the lesions are moist erythematous papuloplaques. In the subsequent subacute stage, a rash showing mild xerotic erythematous to brownish lesions is seen. Finally, in the chronic stage, the lesions show lichenification, which is thickening of the skin due to inflammation and scratching.3 The mainstay treatment involves simultaneously avoiding contact allergens and applying the proper topical steroid.
Syphilis may involve multiple organs, including the skin, and is caused by the bacterium Treponema pallidum. Although it has different clinical stages, the cutaneous manifestation of secondary syphilis occurs 4 to 10 weeks after primary infection. The cutaneous features of secondary syphilis are diverse and, thus, the disease is known as the “great imitator.”3
Most rashes are characterized by scaly erythematous maculopapules on the trunk, extremities, palms, and soles. However, microscopic examination of the scales after KOH treatment usually does not reveal any visible organisms. The diagnosis should be correlated with clinical information, including a thorough medical history and serologic data for syphilis. Because syphilis is a bacterial infection, treatment with appropriate systemic antibiotics such as penicillin, doxycycline, or azithromycin is generally effective. (For more on secondary syphilis, see “Photo Rounds: Pruritic rash on trunk” [J Fam Pract. 2011;60:539-542.])