Although circulating immune complexes have been demonstrated in patients with inflammatory bowel disease, they have not been found in idiopathic or uncomplicated cases. Diagnosis
Erythema nodosum is diagnosed clinically. A biopsy can be taken and examined microscopically to confirm an uncertain diagnosis. Microscopic examination usually reveals a neutrophilic infiltrate surrounding capillaries that results in septal thickening, with fibrotic changes in the fat around blood vessels. A characteristic microscopic finding is radial granulomas, well-defined nodular aggregates of histiocytes surrounding a stellate cleft.Additional evaluation should be performed to determine the underlying cause of erythema nodosum. This may include a full blood count, erythrocyte sedimentation rate (ESR), antistreptolysin-O (ASO) titer and throat culture, urinalysis, intradermal tuberculin test, and a chest x-ray. The ESR is typically high, the C-reactive protein elevated, and the blood showing an increase in white blood cells.The ESR is initially very high and falls as the nodules of erythema nodosum. The ASO titer is high in cases associated with a streptococcal throat infection. A chest X-ray should be performed to rule out pulmonary diseases, in particular sarcoidosis and Löfgren syndrome. Treatment
Erythema nodosum is self-limiting and usually resolves itself within 3–6 weeks. A recurring form does exist, and in children, it is attributed to repeated infections with streptococcus. Treatment should focus on the underlying cause. Symptoms can be treated with bed rest, leg elevation, compressive bandages, wet dressings, and nonsteroidal anti-inflammatory agents (NSAIDs). NSAIDs are usually more effective at the onset of EN versus with chronic disease.Potassium iodide can be used for persistent lesions whose cause remains unknown.
It is typically taken for one to two weeks before entering an area with malaria. Doxycycline and atovaquone/proguanil provide protection within one to two days and may be better tolerated. If a person becomes ill with malaria despite prophylaxis with mefloquine, the use of halofantrine and quinine for treatment may be ineffective. : 4

Malaria treatment
Mefloquine is used as a treatment for chloroquine-sensitive or resistant Plasmodium falciparum malaria, and is deemed a reasonable alternative for uncomplicated chloroquine-resistant Plasmodium vivax malaria. It is one of several drugs recommended by the United States Centers for Disease Control and Prevention. It is not recommended for severe malaria infections, particularly infections from P. falciparum, which should be treated with intravenous antimalarials. Mefloquine does not eliminate parasites in the liver phase of the disease, and people with P. vivax malaria should be treated with a second drug that is effective for the liver phase, such as primaquine. : 4

Resistance to mefloquine
Resistance to mefloquine is common around the west border in Cambodia and other parts of Southeast Asia. The mechanism of resistance is by increase in Pfmdr1 copy number. Adverse effects
Common side effects include vomiting, diarrhea, headaches, and a rash. Severe side effects requiring hospitalization are rare, but include mental health problems such as depression, hallucinations, anxiety and neurological side effects such as poor balance, seizures, and ringing in the ears. Mefloquine is therefore not recommended in people with a history of psychiatric disorders or epilepsy.