Acute Necrotic Arachnidism from spider bite

A woman of 65, obese (BMI = 44.06), with no history of diabetes and allergies but with a mild form of myasthenia gravis (treated only with pyridostigmine po 60 mg every 6 hours), was bitten the evening before hospitalization while cleaning the home cellar by a spider, which, from the description and place where the bite occurred, could probably be identified as the Loxosceles rufescens species. It was not possible to capture the spider. It was also not possible to visit the home cellar, but we had confirmation from local health service of a Loxosceles infestation in neighboring houses.

Initially, the patient did not give much thought to the event given the few or no symptoms but, after the night, early in the morning, given the sharp pain in her right hand, where a bullous lesion had appeared in the middle phalanx of the third finger, accompanied by malaise and fever (38.2°C), she was admitted to a nearby emergency room.

In our Intensive Care Unit, the patient arrived after about four hours owing to the progressive worsening of her general clinical condition. To our observation, after noninvasive monitoring of vital signs, she appeared drowsy (GCS = 8) and tachypneic (respiratory rate = 28/min), with heart rate 90/min and blood pressure = 82/55 mmHg. We could see a circular necrotic skin lesion on the middle phalanx of the third finger of her right hand with erythroderma and oedema of the hand which partially affected the forearm, with strong pain symptoms.

The limb arterial and venous circulation seemed to have stalled, after we performed an ultrasound examination. Telematic support from the National Poison Control Centre in Milan (Italy) confirmed acute necrotic arachnidism from the information provided.

A bolus of saline 30 mL/kg IV, morphine 5 mg IV, and dexamethasone 4 mg were administered to the patient and high flow oxygen via nasal cannula (HFNC) was initiated. Blood tests revealed the following abnormalities: white blood cells 3.3 ∗ 10³  μL, Hb 4.59 mmol/L, platelets 55.000 ∗ 10³  μL, INR 1.72, PT 38.2%, aPTT 121 sec., Procalcitonin 92 ng/mL, and glucose level of 10.67 mmol/L. The blood gas analysis showed a severe metabolic acidosis with pH 7.12, lactate 8.4 mmol/L, and HCO₃ 10 mmol/L.

Endotracheal intubation was initiated along with mechanical ventilation in controlled pressure and invasive monitoring of blood pressure and central venous pressure by placement of a central venous catheter with double lumen 14 Fr catheter. Treatment with norepinephrine at 0.15 mcg/kg/min was started as well as dopamine 8 mcg/kg/min; sedation was achieved via ongoing infusion of remifentanil and midazolam. Prophylaxis against tetanus, specific immunoglobulins, and toxoid tetanus were administered to her. A blood and wound pad culture were taken (which turned out negative after) and broad-spectrum antibiotic coverage was started with Meropenem with 1 gr × 3 doses iv in 24 hours and infusion iv of Daptomycin 4 mg/kg in 30 minutes.

About six hours from admission to the ICU, the oedema had spread to part of the arm with the appearance of erythroderma bullosa (Figure 1) and was clearly distinguished from the initial necrotic lesion on the middle phalanx (Figure 2 and 3). Owing to the development of severe rhabdomyolysis (creatine kinase 2994 U/L and myoglobin 2000 ng/mL), the patient underwent CPFA (coupled plasma filtration adsorption). Transfusion of concentrated red cells was performed due to progressive hemolytic anaemia. Diuresis was kept at values of 1.2 mL/kg/min.

About 12 hours from admission, there was a worsening in tissue condition (Figure 4) , appearance of refractory shock, and disseminated intravascular coagulation leading to death of the patient.