ABSTRACT
The pine processionary caterpillar is an insect that has multiple small, thin hairs around its body as a defense mechanism. These hairs have a hazardous effect on ocular structures and cause a broad range of reactions from conjunctivitis to endophthalmitis, referred to as ophthalmia nodosa. The diagnosis of the disease is based on the patient’s history and the detection of the hairs on ocular structures. In this report, we present a patient with ophthalmia nodosa misdiagnosed as fungal keratitis, and the actual diagnosis was made by in vivo confocal microscopy. We also would like to increase awareness among ophthalmologists about the disease which has a growing distribution area due to climate change.
Introduction
The pine processionary caterpillar, Thaumetopoea pityocampa, is an insect which has abundant fine hairs (also called setae) on its body. It is widely distributed in the pine forests of warmer regions in southern Europe, central Asia, the Near East, and North Africa.1
The hairs of the pine processionary caterpillar have hazardous effects on the human eye, skin, and respiratory tract. The clinical presentation of the resulting ocular disease, referred to as ophthalmia nodosa, can vary in a wide spectrum as conjunctivitis, keratitis, cataracts, uveitis, vitritis, and endophthalmitis.2,3,4,5,6,7,8 The ocular reaction is linked to the mechanical effect of the hairs, direct toxicity of the toxin present inside the hair, and immunoglobulin E-mediated allergic reaction to various caterpillar proteins. The diagnosis of the disease is based on direct visualization of hairs and clinical history of the patient. Since it is a rare condition and the hairs are extremely small and thin, it can be mis- or underdiagnosed during a routine slit-lamp examination.
Our aim in this case report is to present a patient who was misdiagnosed as having fungal keratitis and increase the awareness of ophthalmologists about ophthalmia nodosa, which is expected to be seen at higher frequency with a wider distribution area1 because of global warming.
Discussion
In this article, we report a rare condition called ophthalmia nodosa, which was misdiagnosed as fungal keratitis and later differentially diagnosed using IVCM. Although the disease was first described in the late 1800s, it is not generally well known by ophthalmologists.9 It is caused by a reaction to the hairs of a certain caterpillar which generally lives in pine forests but can be seen wherever pine trees are present. Therefore, the distribution of the disease includes warmer regions in southern Europe, the Near East, and North Africa with an expectation induced by global warming.2
The caterpillar is covered by abundant small, spined urticating hairs as a defense mechanism. When these hairs come into contact with the ocular surface, the clinical presentation may vary in a wide range from allergic conjunctivitis to endophthalmitis, since the hairs can penetrate into the eye.2,3,4,5,6,8,9,10 The diagnosis is based on patient history and clinically detected caterpillar hairs. However, because of the small size of the hairs, they cannot be seen in a routine slit-lamp examination and the diagnosis can be missed. In this patient, IVCM was instrumental in visualizing the caterpillar hairs and discriminating the clinical presentation from infectious keratitis. It was crucial for this patient that the treatment regimen was changed immediately from antifungal to steroid therapy.
In vivo confocal microscopy is a non-invasive, high-resolution, real-time device which is widely used for the diagnosis and treatment follow-up of many anterior segment diseases such as dry eye, keratitis, corneal dystrophies, post-refractive surgery, and post-keratoplasty. To the best of our knowledge, this is the second case in which IVCM was used as a diagnostic tool for caterpillar hairs, which appear as hyperreflective linear needle shapes with multiple small spines.11 The diagnosis of ophthalmia nodosa may be very challenging in areas where these caterpillars are not common, and IVCM might assist with these specific findings.
It is important to be aware of the disease and treat immediately due to the penetration capacity of the hairs. In 2017, an entomology report pointed out that the insect responded to climate changes and insect distribution areas and their natural predators were waxing.1 Therefore, in the near future many ophthalmologists may encounter this entity for the first time, which may result in late or misdiagnosis.
In conclusion, ophthalmologists should be aware of ocular conditions associated with caterpillar hairs and keep them in mind in patients with organic traumas, especially when pine tree contact is present. In patients with insignificant history and clinically undetectable hairs, IVCM can be used as a diagnostic tool.
