ICVA - International Council for Veterinary Assessment Equine Lameness and Neurology Questions and Answers 1 — Questions and Answers
Question 1: A 10-year-old Quarter Horse gelding presents with a 2-week history of asymmetric hindlimb ataxia, gluteal muscle atrophy, and a head tilt. The owner reports the signs are slowly progressive. Which of the following diagnostic approaches is considered the gold standard for an antemortem diagnosis of Equine Protozoal Myeloencephalitis (EPM)?
- Serum antibody testing for Sarcocystis neurona.
- Western blot analysis of cerebrospinal fluid (CSF) alone.
- Response to a course of antiprotozoal treatment.
- Paired serum and CSF antibody testing to demonstrate intrathecal antibody production. (Correct answer)
Correct answer: Paired serum and CSF antibody testing to demonstrate intrathecal antibody production.
The most accurate method for diagnosing EPM in a living horse involves comparing antibody levels in both serum and cerebrospinal fluid (CSF). A higher antibody titer in the CSF compared to the serum (a high serum:CSF ratio) indicates that antibodies are being produced within the central nervous system, which is highly suggestive of an active infection. Serum testing alone only indicates exposure to the parasite, not active disease, as a high percentage of healthy horses are seropositive. CSF testing alone can be misleading due to potential blood contamination. While response to treatment is sometimes used, it is not a definitive diagnostic method.
Question 2: A veterinarian is performing a lameness examination on a horse with a right forelimb lameness. The lameness is completely resolved after a palmar digital nerve (PDN) block. Which of the following structures is LEAST likely to be the source of pain?
- Navicular bone
- Distal interphalangeal (coffin) joint
- Proximal interphalangeal (pastern) joint (Correct answer)
- Digital cushion and sole
Correct answer: Proximal interphalangeal (pastern) joint
A palmar digital nerve (PDN) block, or heel block, desensitizes the palmar third to one-half of the foot. This includes the navicular bone, navicular bursa, digital cushion, sole, frog, and portions of the coffin joint and deep digital flexor tendon. The proximal interphalangeal (pastern) joint is innervated by more proximal nerves and would not be fully desensitized by a PDN block. Pain originating from the pastern joint would typically be resolved with a more proximal block, such as an abaxial sesamoid nerve block.
Question 3: A 2-year-old Thoroughbred colt presents with symmetric hindlimb ataxia that is worse when the horse's head is elevated. The colt is bright and alert with a normal appetite. Radiographs of the cervical spine reveal narrowing of the vertebral canal at C3-C4. What is the most likely diagnosis?
- Equine Motor Neuron Disease (EMND)
- Equine Protozoal Myeloencephalitis (EPM)
- Cervical Vertebral Stenotic Myelopathy (CVSM) (Correct answer)
- Tetanus
Correct answer: Cervical Vertebral Stenotic Myelopathy (CVSM)
Cervical Vertebral Stenotic Myelopathy (CVSM), also known as Wobbler Syndrome, is a common cause of symmetric ataxia in young, rapidly growing horses, particularly Thoroughbreds and Quarter Horses. The clinical signs, including symmetric hindlimb ataxia that worsens with neck extension (head elevation), are classic for this condition. The diagnosis is supported by imaging, such as radiographs or a myelogram, which demonstrates narrowing of the spinal canal and subsequent spinal cord compression.
Question 4: Which of the following clinical signs is most characteristic of stringhalt in a horse?
- Difficulty backing up with hindlimb hyperextension.
- Symmetric hindlimb weakness and proprioceptive deficits.
- Involuntary, spasmodic hyperflexion of one or both hindlimbs during the walk. (Correct answer)
- Progressive, symmetric muscle atrophy of the back and hindquarters.
Correct answer: Involuntary, spasmodic hyperflexion of one or both hindlimbs during the walk.
Stringhalt is a neuromuscular condition characterized by a sudden, involuntary, and exaggerated upward flexion of one or both hindlimbs during movement, most notably at the walk. The leg is quickly snapped toward the abdomen and then slapped back down on the ground. This is distinct from shivers, which is more often seen when the horse is backing up and involves abduction of the limb. Symmetric ataxia is more typical of spinal cord disease, and progressive muscle atrophy is seen in conditions like EMND or EPM.
Question 5: A 5-year-old Warmblood gelding used for dressage is presented for poor performance and a subtle right hindlimb lameness. The lameness is not obvious on a straight line but is exacerbated when the horse is lunged on a hard surface with the affected limb to the inside. A low four-point nerve block fails to improve the lameness, but a subsequent tibial and peroneal nerve block significantly improves the gait. Pain is most likely originating from which region?
- The foot
- The fetlock
- The proximal suspensory ligament/proximal cannon bone region
- The hock (tarsus) or structures distal to it (Correct answer)
Correct answer: The hock (tarsus) or structures distal to it
A low four-point block desensitizes the fetlock and all structures distal to it. Since the lameness did not improve with this block, the source of pain is located more proximally. The tibial and peroneal nerves provide sensation to the hock and the distal limb. A positive response to a tibial and peroneal nerve block after a negative low four-point block localizes the source of pain to the hock region. If the lameness improved only after the tibial nerve block, the proximal suspensory ligament would be a primary suspect.
Question 6: A veterinarian is presented with a horse exhibiting sudden, severe, non-weight-bearing lameness of the left forelimb. The digital pulses are bounding, and the horse is reluctant to move. There is a focal area of sensitivity to hoof testers over the sole. Which of the following is the most common cause for these acute and severe signs?
- Laminitis
- Navicular syndrome
- A subsolar abscess (Correct answer)
- Osteoarthritis of the coffin joint
Correct answer: A subsolar abscess
A subsolar abscess is one of the most common causes of acute, severe, non-weight-bearing lameness in horses. The classic presentation includes a sudden onset, bounding digital pulses, and focal sensitivity to hoof testers, which help pinpoint the location of the abscess under the sole. While laminitis also causes severe lameness and bounding pulses, it often affects both front feet and presents with a characteristic "rocked-back" stance. Navicular syndrome and osteoarthritis are typically chronic conditions that cause more of a progressive, less severe lameness.
ICVA - International Council for Veterinary Assessment Equine Lameness and Neurology Questions and Answers 1
A 10-year-old Quarter Horse gelding presents with a 2-week history of asymmetric hindlimb ataxia, gluteal muscle atrophy, and a head tilt.
The owner reports the signs are slowly progressive.
Which of the following diagnostic approaches is considered the gold standard for an antemortem diagnosis of Equine Protozoal Myeloencephalitis (EPM)?