Symptoms of SMON
SMON is the acronym for Subacute myelo-optico neuropathySMON has been ascertained as drug poisoning caused by the adverse effects of chinoform (clioquinol), an antiflatulent. No new patients have been detected since marketing of this drug was prohibited. The male-to-female ratio of SMON patients is 1:3, with more female patients.
Gastroenterological symptoms such as diarrhea and stomachache occur first. Separate from the original abdominal symptoms leading to the use of the drug, symptoms specific to SMON may also occur, including severe stomachache, abdominal distention and constipation,. Subsequently, acute to subacute neuronal symptoms occur. Numbness starting at the toe frequently occurs as a primary symptom and gradually spreads upward to the navel and chest. Strong numbness is likely to appear bilaterally and distal dominantly in the lower extremities. Patients often complain of electic shock, a tingling sensation, an uncomfortable feeling on the sole of the foot (as if something is stuck to it), or a tight feeling. Superficial sensation and deep sensation are also objectively impaired.
Moreover, motility disturbance is observed in almost half of patients. The muscles of the lower extremities are weakened, and ambulation is often disturbed. Patients are at high risk of falling from ataxia due to disturbance of proprioception (the sense of one’s limbs in space). Lower extremity deep reflex is accelerated, and a positive Babinski sign is found in some cases. The upper extremities may also be impaired in severe cases.
Impaired visual acuity is observed in 20 to 30% of patients. It may lead to blindness in the most severe cases, and data indicates that approximately 5% of patients have a complete loss of sight. Autonomic nerves are also impaired, and cold feet, urinary disturbances such as incontinence, and defecation disturbances including constipation, diarrhea, or alternation of diarrhea and constipation, are observed.
Other than neuronal symptoms, a green-coated tongue and greenish stool were known as symptoms of SMON. An analysis of green crystals found in the urine of patients served as an important clue to pinpointing chinoform as the cause of the disease.
After discontinuation of chinoform use, symptoms gradually improve but sequalae remain in sensation, gait and vision to a various extent. SMON patients have aged, with a current mean age of 80 years, and various concomitant symptoms including cataracts, hypertension, spinal disease and extremity joint disease now accompany the original symptoms of SMON. Furthermore, mental symptoms such as anxiety and frustration, hypochondria, and depression are occasionally observed. While the occurrence of dementia has been considered to be less among SMON patients, it is increasing yearly.
Although the number of patients with juvenile-onset SMON is small, their symptoms are slightly different from those of patients with adult-onset SMON, and impaired visual acuity and spastic paralysis may be more apparent in this population.
- Research Committee on SMON
- Research representative:
Masaaki Konagaya, Director, NHO Suzuka National Hospital
3-2-1 Kasado, Suzuka-shi, Mie-ken, 513-8501
Phone: +81-59-378-1321
