Lower-leg Cellulitis-like Manifestations of Erythema Nodosum Induced by Chlamydophila pneumoniae Infection.

Sir,

Although rare, when erythema nodosum (EN) mimics lower-leg cellulitis, it is sometimes difficult to reach the correct diagnosis. We report such a case, in which the causal microorganism was determined to be Chlamydophila pneumoniae (CP).

A 42-year-old Japanese man without a significant medical history presented with a tender erythematous swollen right lower leg [Figure 1a]. His body temperature was 37.8°C, and routine laboratory testing showed an elevated white blood cell (WBC) count (11,700/μL) and a C-reactive protein level of 0.78 mg/dL. Lower leg cellulitis was suspected, and cephalexin was prescribed. Eight days later, an erythematous rash appeared on the left lower leg [Figure 1b] accompanied by a fever of 38.0°C. Afterward, the patient had recurrent episodes of erythematous edema affecting both legs, associated with fatigue, fever, night sweats, arthritis, and myalgia. A skin biopsy demonstrated septal panniculitis with vasculitis; infiltration of lymphocytes and neutrophils into the adipose septa and paraseptal blood vessel walls [Figure 1c and d]. The epidermis and upper dermis showed no significant changes. Although palpable nodules were not recognized, the possibility of EN was raised. Although he denied having respiratory symptoms and his chest X-ray was unremarkable, laboratory testing revealed an elevated anti-CP immunoglobulin M index of 2.12, suggesting an acute CP infection. Minocycline hydrochloride 100 mg/day was initiated and his clinical problems improved within 10 days. He has been free from recurrence since.

Figure 1

(a) At the time of the initial presentation, tender erythematous swelling of the patient's right lower leg appeared as cellulitis. (b) Eight days after his initial presentation, an erythematous rash was seen on the left lower leg. (c) H and E, ×40, section of a skin biopsy revealed infiltration of lymphocytes and neutrophils into the adipose septa and paraseptal blood vessels. (d) Infiltration of vessel walls mainly with lymphocytes (×100)

When typical nodular lesions are not apparent, EN could be misdiagnosed and managed as cellulitis.[123] Tender erythematous swelling repeatedly affecting both legs and not responsive to cephalosporins is atypical for cellulitis. In such a situation, EN is a diagnostic possibility, and skin biopsy is recommended.

CP is one of the infectious organisms associated with EN, but its association is rare. Cribier et al. reported only two of 54 patients with EN had the infection.[4] Aydın-Teke et al. examined 39 pediatric EN cases and found only one had CP with concomitant streptococcal infection.[5] There are only three English-language case reports describing four patients, and including our case, we analyzed five patients. They were comparatively young, aged 29.8 ± 13.2 years (range: 11–42 years, median; 37 years). Tender nodules were not observed in two cases and thus atypical EN was diagnosed. Four patients suffered from a high fever and three had myalgia. Respiratory symptoms, such as cough, were observed in two patients, and a chest X-ray revealed abnormal findings in two patients. Laboratory examinations revealed a high erythrocyte sedimentation rate in four patients, whereas an elevated WBC count was observed only in one patient. All the patients were given tetracyclines or macrolides, and they subsequently improved.

Considering the fact that approximately 60–70% of healthy individuals are seropositive for CP,[6] the association of CP with EN might be higher. When EN is diagnosed, serological investigation for CP infection seems worth performing, especially in comparatively young patients. In this case, paraseptal vasculitis was intense when compared to typical EN. As reported previously, vasculitis might be a feature of CP infection-associated panniculitidies.[7]

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