What is the pathognomonic sign of Measles?

1.

Gans, Hayley A. (2025). In Nelson Textbook of Pediatrics (pp. 1958). DOI: 10.1016/B978-0-323-88305-4.00293-5

Measles is a serious infection characterized by high fever, an enanthem, cough, coryza, conjunctivitis, and a prominent exanthem (Fig. 293.2). After an incubation period of 8-12 days, the prodromal phase begins with a mild fever followed by the onset of conjunctivitis with photophobia, coryza, a prominent cough, and increasing fever.Koplik spotsrepresent the enanthem and are the pathognomonic sign of measles, appearing 1-4 days before the onset of the rash (Fig. 293.3). They first appear as discrete red lesions with bluish-white spots in the center on the inner aspects of the cheeks at the level of the premolars. They may spread to involve the lips, hard palate, and gingiva. They also may occur in conjunctival folds and in the vaginal mucosa. Koplik spots have been reported in 50–70% of measles cases but probably occur in the great majority. Symptoms increase in intensity for 2-4 days until the first day of the rash. The rash begins on the forehead (around the hairline), behind the ears, and on the upper neck as a red maculopapular eruption. It then spreads downward to the torso and extremities, reaching the palms and soles in up to 50% of cases. The exanthem frequently becomes confluent on the face and upper trunk (Fig. 293.4). With the onset of the rash, symptoms begin to subside. The rash fades over about 7 days in the same progression as it evolved, often leaving a fine desquamation of skin in its wake. Of the major symptoms of measles, the cough lasts the longest, often up to 10 days. In more severe cases, generalized lymphadenopathy may be present, with cervical and occipital lymph nodes especially prominent.

Measles should be suspected in the presence of fever and a maculopapular (nonvesicular) rash. Measles has a 7- to 21-day incubation period, with onset of fever and malaise (prodrome), as well as the more specific combination of a “croupy or brassy” cough, coryza, conjunctivitis, and photophobia beginning about 10 days after exposure (Fig. 338-1). Koplik spots (Fig. 338-2),which are raised bluish-white papules inside both cheeks, may appear at this time; though pathognomonic, they are often missed or misdiagnosed as thrush, and they fade as the rash emerges. The classic erythematous blanching maculopapular rash begins on the face, spreads down the body, and becomes confluent and darker in color over days (Fig. 338-3A).The rash is more subtle in dark-skinned patients (Fig. 338-3B), in whom the diagnosis may be delayed. In malnourished and immunosuppressed individuals, a prolonged desquamating dermatitis is commonly seen (Fig. 338-3C). Body temperature is high, 39° to 40.5° C, beginning with the prodrome and continuing at least 4 days into the rash. Patients are contagious to others from 4 days prior until 4 days after onset of the rash. As the rash darkens and fades, the skin will often flake and peel. In individuals with incomplete postimmunization protection, clinical symptoms may be milder, with less fever and catarrh, a later onset (12 to 16 days), and markedly reduced infectivity.

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Measles (Rubeola), Elsevier ClinicalKey Clinical Overview

Diagnosis Patients often appear quite ill Conjunctival injection may be present Cervical lymphadenopathy may be present Koplik spots Pathognomonic for measles Often visible before rash eruption Lesions are small and white with a blue-gray center on an erythematous base Typically located adjacent to the molars on buccal mucosa; may be observed elsewhere on oropharyngeal mucosa Rash Often morbilliform early in its evolution May become confluent, especially on head and neck Palms and soles are often involved Becomes more brown than red over course of several days before fading Areas of desquamation may develop Less prevalent respiratory signs in young children Stridor associated with crouplike presentation Scattered, coarse wheezing; tachypnea; and retractions associated with bronchiolitislike presentation