1. Nahar, Ludmila
  2. Brodell, Robert T.

Article Content


Chief complaint: Sudden onset of pruritic rash on the trunk and extremities with linear eruption on the forearms.


A 26-year-old developed a sore throat 5 days before the onset of this rash. A rapid antigen streptococcus test confirmed this was a streptococcal sore throat. Amoxicillin 500 mg twice daily was started 3 days ago anticipating a 7-day course. The patient began developing waxing and waning pruritic welts on the trunk and extremities in the past 12 hours. Linear lesions appeared on the forearms in the past 3 hours prompting an urgent care visit (Figure 1).

Figure 1 - Click to enlarge in new windowFIGURE 1. Transient, pruritic, erythematous linear eruption on the arms.

Prior treatment:


* Prior biopsy: None


* Allergies: No known drug allergies


* Skin history: No history of similar rashes or any past medical problems


* No other significant laboratory/study findings




One image provided showed scattered 1- to 5-cm urticarial plaques on the trunk and extremities with parallel, linear, raised, blanching, erythematous 2-mm wide streaks on the dorsal forearms.



Fully satisfactory.




Linear lesions are uncommon in dermatology. Conditions that arise from the inside out generally produce patchy rashing. A key distinguishing feature in this case of linear welting or hiving (dermatographism) is the waxing and waning of lesions, with none lasting longer than 24 hours. The lesions can be reproducibly produced in such patients by firmly rubbing the skin.



Skin Care Recommendations

Avoidance of rubbing and scratching is important in patients with dermatographism. Application of ice in a plastic bag is one way to reduce localized itching.


Medication Recommendations

Fexofenadine 180 mg orally each morning and cetirizine 10 mg orally nightly. One week after clearing of hiving, the patient was instructed to taper off one antihistamine and then the other. The amoxicillin was also discontinued because it was a possible cause of urticaria, and azithromycin 500 mg daily for 5 days was prescribed to ensure that the streptococcal sore throat was adequately treated.



Refer to dermatology clinic for evaluation (face-to-face) and consideration of a skin biopsy if the lesions do not continue to wax and wane in hours or if they fail to clear in 6 weeks. Fixed hives can be an indication of urticarial vasculitis.



Waxing and waning linear urticarial lesions at the site of scratching are pathognomonic of dermatographism (Danielsen, Ortiz, & Symington, 2018). This is common in patients with urticaria. Hundreds of causes of urticaria have been documented including drugs, infections, inhalants, ingestants, blood transfusions, internal malignancies, physical factors (pressure, ultraviolet radiation, cold, sweating, exercise, water, and vibration), and stress (Gloster, Gebauer, & Mistur, 2016). Hives are produced by diverse vasoactive mediators, predominately histamine, released from mast cells on activation (Deacock, 2008). Most urticaria are acute, and the condition lasts less than 6 weeks. Chronic urticaria persisting for longer than 6 weeks usually prompts a more aggressive workup to identify the cause, when possible. Antihistamines are safe to ameliorate the effects of histamine release and can be used in combinations for a greater effect (Monroe, 2005; Sanchez-Borges & Ansotegui, 2019). An alternative approach is utilizing up to four times the Food and Drug Administration recommended dosing, which has been shown to be both safe and effective (Zuberbier, 2012).


In this case, the streptococcal sore throat is the most likely cause of urticaria. Penicillin is less likely, but a possible cause. A substitute antibiotic with an unrelated chemical structure was used to eradicate the streptococcal sore throat, and the patient's hives and dermatographism were quickly controlled with antihistamines. They were tapered off after 2 weeks, and the hives and dermatographism did not recur. Scratch testing to penicillin at the allergist could be recommended before initiating treatment with penicillin in the future. Of note, this patient did not have the classic maculopapular rashing of amoxicillin in the setting of mononucleosis, and such measles-like rashes are not associated with dermatographism.


The Differential Diagnosis

The vast majority of rashes are not linear. Exceptions include rashing in bands representing dermatomes such as herpes zoster (shingles) and koebnerization in psoriasis, lichen planus, and lichen nitidus where external trauma induces linear eruptions. Pseudo-koebnerization can be seen in warts and molluscum where the infectious agent is inoculated in a line when these lesions are scratched. Finally, an allergic contact dermatitis, most commonly because of poison ivy, can appear as a linear papulovesicular eruption. None of these lesions disappears in hours, as is the case in dermatographism.




Danielsen R. D., Ortiz G., & Symington S. (2018). Chronic urticaria: It's more than just antihistamines! Clinician Reviews, 28(1), 36-43. [Context Link]


Gloster H. M., Gebauer L. E., & Mistur R. L. (2016). Urticarias. In Absolute dermatology review (pp. 449-453). Cham, Switzerland: Springer. doi: [Context Link]


Monroe E. (2005). Review of H~1 antihistamines in the treatment of chronic idiopathic urticaria. Cutis-New York, 76(2), 118. [Context Link]


Sanchez-Borges M., & Ansotegui I. J. (2019). Second generation antihistamines: An update. Current Opinion in Allergy and Clinical Immunology, 19(4), 358-364. [Context Link]


Zuberbier T. (2012). Pharmacological rationale for the treatment of chronic urticaria with second-generation non-sedating antihistamines at higher-than-standard doses. Journal of the European Academy of Dermatology and Venereology, 26(1), 9-18. [Context Link]


1 The standardized teledermatology reader format is available for authors on the journal's Web site ( and on the submissions Web site online at [Context Link]