A 6-year-old boy is brought to the office by his mother due to fever, pruritic rash, and joint pain. The rash began 2 days ago and has spread to his trunk and arms. The patient has also had pain in the wrists and ankles. He was diagnosed with streptococcal pharyngitis 9 days ago and is on his second to last day of oral penicillin. Temperature is 38.8 C (101.8 F). Physical examination shows an uncomfortable-appearing boy with a diffuse rash on the arms and back. There are palpable lymph nodes in the cervical, axillary, and inguinal regions. The wrists and ankles are tender to palpation but are not swollen or erythematous. The remainder of the physical examination is normal. Which of the following is the most likely diagnosis?

Question

A 6-year-old boy is brought to the office by his mother due to fever, pruritic rash, and joint pain.  The rash began 2 days ago and has spread to his trunk and arms.  The patient has also had pain in the wrists and ankles.  He was diagnosed with streptococcal pharyngitis 9 days ago and is on his second to last day of oral penicillin.  Temperature is 38.8 C (101.8 F).  Physical examination shows an uncomfortable-appearing boy with a diffuse rash on the arms and back.  There are palpable lymph nodes in the cervical, axillary, and inguinal regions.  The wrists and ankles are tender to palpation but are not swollen or erythematous.  The remainder of the physical examination is normal.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d744_a69e_bc81_31a19067f421_MD0003_00 This boy took penicillin for several days and then developed symptoms (eg, fever, urticaria, arthralgia) of serum sickness-like reaction (SSLR). Although the presentation of SSLR closely resembles serum sickness (SS), the underlying cause differs. SS, classically triggered by exposure to foreign proteins (eg, antitoxins, murine/chimeric monoclonal antibodies), is due to the generation of high-titer immune complexes (ICs), the deposition of ICs in tissue, and the excessive activation of the classical complement cascade. In contrast, SSLR is not associated with high-titer ICs or excessive complement activation; although the exact etiology is unclear, most cases may reflect drug-related hapten formation or direct lymphocyte cytotoxicity triggered by exposure to beta-lactam (eg, cefaclor, penicillins) or sulfa (eg, trimethoprim-sulfamethoxazole) drugs. Both SS and SSLR present with: Fever Urticarial rash: intensely pruritic plaques that spare the mucous membranes and typically persist for >24 hours Arthralgia: polyarticular joint pain that worsens with movement and palpation. Signs of arthritis (eg, overlying erythema, warmth, edema) are not typically present but may occasionally occur Some patients also have mild proteinuria or diffuse lymphadenopathy. Compared to SS, SSLR is usually less severe (eg, low-grade fever, less likely to cause systemic manifestations) and is more common in children. Manifestations typically begin within 5-14 days of medication initiation and resolve spontaneously with medication discontinuation. (Choice A) Acute rheumatic fever is marked by fever, erythema marginatum rash, and arthritis. However, the arthritis is migratory and accompanied by marked joint swelling; the rash is nonpruritic; and many patients have carditis. In addition, rheumatic fever is extremely rare in patients who receive prompt treatment for streptococcal pharyngitis. erythema marginatum (Choice B) Anaphylaxis is a IgE-mediated type I hypersensitivity reaction that occurs within minutes of drug exposure. Although urticarial rash is common, patients also typically have hypotension, wheezing, gastrointestinal symptoms, and/or angioedema. Arthralgia and lymphadenopathy would be atypical. (Choice C) Henoch-Schönlein purpura is a systemic IgA-mediated vasculitis that typically occurs after upper respiratory infection. Although arthralgia and fever are common, patients usually have palpable purpuric rash, not urticaria. palpable purpuric rash (Choice D) Scarlet fever can accompany streptococcal pharyngitis. Although the condition often causes fever and rash, it presents as a diffuse sandpaper-like rash accompanied by a "strawberry" tongue. Urticaria and arthralgia would be atypical. sandpaper-like rash (Choice F) Stevens-Johnson syndrome is a type IV hypersensitivity reaction triggered by medications (eg, sulfa drugs, anticonvulsants). Although high fever and rash are common, the rash is typically sunburn-like and diffuse. In addition, most patients have painful hemorrhagic oral erosions. Educational objective: Serum sickness-like reaction is most common in children and is typically triggered by beta-lactam (eg, cefaclor) and sulfa drugs. Symptoms begin 5-14 days after exposure and include urticarial rash, arthralgia, lymphadenopathy, and low-grade fever. Manifestations resolve with withdrawal of the offending agent. References: Urticaria mimickers in children. (http://www.ncbi.nlm.nih.gov/pubmed/24552410) Serum sickness-like reaction to cefuroxime: a case report and review of the literature. (http://www.ncbi.nlm.nih.gov/pubmed/17763603)

A 6-Year-Old Boy Is Brought to the Office by His