What is the differential diagnosis of plant-related mouth pain?
The oral mucosa is composed of superficial layers of mucin and epithelial cells that lie over the dermis and connective tissue. Local immune cells, including mast cells and Langerhans cells, reside in the deeper layers. The differential diagnosis of plant-based mouth pain can be divided into mechanical, chemical, and thermal causes.
Mechanical Causes. Causes of mechanical plant-based oral pain include structural damage when foreign matter, such as barbs, sharp leaves, or hard seeds, pierce the layers of the oral mucosa.
Chemical Causes. Chemical-related causes of oral pain include caustic ingestion, for example from detergents or cleaning agents that contaminate the broth. Araceae, such as taro or arum, have sharp calcium oxalate crystals tipped with phospholipases and proteases that cause mechanical pain on piercing mucous membranes, and chemical pain by enzymatically degrading epithelium and mucosa. Both chemical and mechanical irritation can lead to an inflammatory response. Raw taro can cause irritant contact stomatitis as the raphides pierce the oral mucosa. It can also cause allergic stomatitis if antigens related to the phospholipases or proteases are presented to Langerhans cells.9
Thermal Causes. The hot temperature of the ingested broth could cause thermal injury, but the injury is likely to be more diffuse.
How common is taro exposure, and how is it treated?
From 1995 to 1999, 15 cases of taro poisoning were reported to the Drug and Toxicology Information service in Zimbabwe.10 From 2005 to 2009, 21 out of 31 cases reported to the Hong Kong Poison Control Center involving gastrointestinal irritation involved the consumption of Colocasia fallax, a form of taro more common in Tibet, the Himalayas, and northern Indochina.7 Of the 31 cases, six patients were treated with diphenhydramine, epinephrine, and dexamethasone for angioedema.
From 2011 to 2013, two cases of mouth irritation and swelling after eating raw taro leaves were reported to the British Columbia Poison Control Center.11 Those two patients were observed for 6 hours without specific treatment and discharged.
Case Conclusion
Due to concerns of the potential for anaphylaxis, both patients were treated intravenously with 50 mg diphenhydramine and 10 mg dexamethasone. The husband was also given 650 mg acetaminophen orally for pain relief; his wife declined pain medication. Laboratory evaluation, including a complete blood count, basic metabolic panel, liver function panel, and urinalysis were ordered for both patients; all results were within normal limits for both patients.
After an uneventful 6-hour observation period, both patients were discharged home with instructions to return to the ED if they develop any signs of allergic reaction and to call emergency medical services for any sign of anaphylaxis.